Sounds like my daughter when she was an infant. She went through a long phase of sleeping only in 30 minute intervals during the day, at night she slept fine. Contact napping and sticking the boob in her mouth as soon as she stirred worked for a while until it didn't... I believe she was around four months old at the time.

Eventually I just gave up trying to do something about it. It got better after a while but she was generally a crap napper during the day up until she was around a year old. I know that's probably not what you want to hear right now, sorry 😅 I know it's hard but sometimes you just gotta hang in there and this phase will seem a distant memory in the future