Darcie Pennington, 18, was "shocked and upset" after nurses told her she could not feed her four-month-old baby, Vincent, in public during a visit.
The mum-of-one, from Blackburn, had driven for two hours to see her grandma, who was in the Royal Liverpool Hospital for specialist cancer care.
"I've fed everywhere, shopping centres, shops, cafes - and I've never had a problem like this before," Pennington said.
"I can't believe this attitude came in a hospital, and from nurses."
Pennington said during the Saturday visit to see her grandma, she had broken off from feeding to settle her baby when a nurse approached her.
"She came up and said: 'You need to sit in a private room.' She said I was making the gentlemen feel uncomfortable," Pennington said.
"I was shocked by what she had said and told her politely that I am legally allowed to feed my child wherever I like.
"And I considered I was feeding in a fairly private area anyway, with my back to the room.
"My baby is very young and relies on my milk, he feeds on demand - which is quite often.
"We only have a couple of hours to see my nan, I don't want to spend the majority of that time in a different room away from her.
"We had travelled a long way to be there, there was no way I could have left my baby at home. He has to be with me if he needs a feed.
"Another nurse then came up and said they were protecting my dignity. I asked if dignity would need to be protected if I was feeding with a bottle, and I was told that no, because feeding with a bottle was not sexual.
"I asked which part of breastfeeding she considered to be sexual.
"When I went to sit back down to resume the feed the nurse stormed over and rudely tugged the curtain around us. I was incredibly hurt, upset and embarrassed.
"I asked for her name and asked her why she wasn't promoting breastfeeding. She didn't say anything.
"I'm lucky in that I'm confident in my feeding, what if it was someone who wasn't so confident? Something like this could put them off.
"They made me feel like I wasn't doing the right thing."
Pennington said she's since had a phone call from the head nurse who has told her she was "disgusted" by the other nurses' behaviour and that she would "get to the bottom of it".
Deputy chief nurse at the hospital, Colin Hont, apologised and said that breastfeeding is not something hospital staff would usually disapprove of.
"We are aware of a complaint made by Miss Pennington and we are currently looking into the matter," he said.
"We fully support breastfeeding and visitors to our hospital are welcome to breastfeed where they choose to and feel most comfortable.
"We also offer private spaces for mothers who wish for privacy when breastfeeding.
"We always apologise for any distress that has been caused."
A spokesperson from breastfeeding support group La Leche League GB said: "We were surprised to hear that a mother had been told she should go to a private room to breastfeed her baby.
"It's entirely legal to breastfeed in public spaces anywhere in the UK and the Equality Act of 2010 states that treating a woman unfavourably because she is breastfeeding a child of any age is considered sex discrimination.
"This applies to any premises providing services to the public and the Act makes it clear a woman must not be discriminated against, harassed or victimised because she is breastfeeding.
"This unfortunate incident may highlight the need for all hospital staff to be kept fully up-to-date with the fact that a breastfeeding mother is not required to cover herself or go to a specific room and this will hopefully ensure similarly distressing incidents are avoided in future."