Amie Jones, 21, of Harpurhey, Manchester, said the mental health condition caused her to have intense panic attacks and hallucinations.
Jones wants to raise awareness of the illness, which can affect a woman after she has a baby, so other mothers "don't feel alone".
"I had no idea what post-partum psychosis was," Jones said. "I'd thought I was hearing a voice in my head, like in a film where you have two twins, one evil and one good.
"It was my voice in my head, but an evil version."
Jones revealed how even finding out she was pregnant, at the end of December 2013, was a bit of a shock.
The year before falling pregnant, she had been diagnosed with endometriosis, a common condition where tissue that behaves like the lining of the womb is found outside the womb.
She assumed this would make it harder for her to have children.
"I was 18 and panicked. I crumbled. I punched my stomach, my head was all over the place," she said. "It was not what I wanted.
"I had so much doubt in my mind, that I should just end my life now. The baby was the only thing keeping me from doing it."
Jones considered having an abortion just four days after she found out she was pregnant, but decided against it.
"Part of me felt ungrateful, because I should have been happy to have a child, but I wasn't ready," she explained.
"I kept asking myself questions. Would I be a good mum? Would I be able to give it up for adoption? Would I be able to love my child?
"I wanted to prove to people I'd be an amazing mum. So I said I loved it when my baby kicked, but that was all a front.
"I actually felt mortified and depressed and I worried I would not be able to bond with my baby.
"I had a psychiatrist that I saw every four weeks who was lovely, but I didn't want to tell her that I didn't think I could love my baby, as I didn't want social services getting involved."
Jones said towards the end of her second trimester in April 2014 she felt so low that she went to see a specialist mental health midwife and psychiatrist at St Mary's Hospital in Manchester, who diagnosed her with bipolar disorder and increased her dosage of the anti-depressant Prozac.
Four weeks before her due date, she also confessed to her mental health psychiatrist that she could not cope anymore.
"I begged her to get the baby out of me," she said. "I'd been on maternity leave so had spent a lot of time alone with my thoughts. I'd think about giving birth and then running away.
"I was numb, and wanted to end my own life. Now when I think about that, it upsets me."
Jones was put in the care of the crisis team at Ramsgate House - a community mental health clinic in Salford - where nurses would check on her every day.
She was induced two weeks early on 26 July 2014, at the St Mary's Hospital in Manchester, with her ex-boyfriend and mum Helen Jones, 47, by her side.
Jones said: "After being in labour for 21 hours Oscar was born on 27 July.
"I felt awful that I didn't feel anything. When I took Oscar home my heart was constantly racing, I was always panicked and on edge.
"I had no clue what I was doing and I couldn't look at him when I was feeding him.
"I'd shake a toy in front of him because I thought that's what I was meant to do, but I was not connected.
"I felt like I needed help, that I couldn't do it.
"To me it felt like Oscar was crying all the time, but in hindsight he was a good boy."
When Oscar was 11 days old Jones' health visitor went to see her and she asked for help.
The midwife phoned a support worker from Sure Start, a government programme that provides a range of support services for parents and children under the age of four.
The support worker took her to hospital.
At the Salford Royal NHS Foundation Trust, the young mum was having panic attacks and trouble breathing, and was immediately referred to a mental health unit.
"I thought they were going to lock me up and take my son away because I didn't have a bond with him," she said.
"I was feeling suicidal, but what was stopping me ending my life was having Oscar with me.
"A voice in my head said, 'Right, when the nurse leaves the room, just run.'
"When I think about it now, it seems sinister – planning to run away and leave my baby so I could go kill myself."
Jones was voluntarily admitted to a psychiatric hospital at the mother and baby unit in Manchester's Wythenshawe Hospitaland remained there from mid-August 2014 until November 2014.
She said: "At the time it seemed dire, but now I see it was a fantastic ward with fantastic nurses.
"I could see Oscar when I wanted, but I couldn't be with him alone.
"When I arrived they took anything dangerous away from me, but I would scratch my wrists when Oscar was down in the nursery.
"It was on the second day that a psychiatrist diagnosed me with post-partum psychosis and put me on anti-psychosis medication and sleeping tablets."
Jones said she would frequently hear voices in her head and have panic attacks during this time, but said the support she received while at the Wythenshawe Hospital was amazing.
To help her, medics tried a range of techniques including mindfulness, going to the gym and taking her to Pets at Home because they knew she loved animals.
They ran sessions to help her bond with her baby, guiding her through every day tasks with Oscar such as bathing or massaging him.
They also ensured she had taken her medication each day and asked what her thoughts were and how they could help, supporting her all the time.
In November 2014 she was allowed to return home and had to adjust to looking after her baby alone. She had split up with her former boyfriend, Oscar's dad, in July 2015.
Now she is living with her current partner Rob and is doing much better.
Gradually, with all the support she has received, she has formed a bond with her baby.
"I'm a lot happier now, but I'm still not 100% better," she said.
"I'm still on lots of anti-psychotic medication, as well as medication to help my depression, and I have my community psychiatric nurse from Ramsgate House that I can call.
"Rob has been amazing and he's great with my son.
"I love the bones off Oscar now. I never thought I would feel this way about him. When he goes to stay with his dad I miss him.
"I still have down days and get nervous in public with him, but at home I'm in my element.
"I see my future with Oscar being really positive.
"He's so clever; I can't wait to see him at school and to take him on holiday.
"I'm proud of where I am in comparison to last year, and I'd happily have another child."
If you need support contact the Samaritans on 116 123 (UK).