Why does my mum just never seem interested in me?

My mum hardly ever answers my calls/messages and is happy hardly ever seeing me. I'm 23 and bought and moved into my first house with my boyfriend 7 months ago. Since buying the house in April we have had 2 national lockdowns and 1 local lockdown but my mum has only come to visit me twice, once to see the house just after we bought it and another when I was having a bad flare up after coming out of hospital. Other than that I've hardly seen her, I lived at my nans from 18 to 22 and it was the same then. I was always the one going to visit my mum and asking her to meet up etc. She just never makes an effort, yes I understand she has 4 other children (17, 13, 11 & 7) but the only time she calls me is to ask me to either lend her money or pick the kids up from school. She never asks how my appointments go (I have a rare muscle disease & rheumatoid arthritis), how our house renovations are going or just pops up for a cup of tea (I live 5 minutes away from her). It really breaks my heart because when I go to her house, it's never the right time, shes always busy and it's been like this for the past 6 years. Meanwhile I cannot even count the number of times my boyfriends family have visited, they pop up every week for a chat and also invite us to theirs. I have always been independent but when I just want to call my mum for a chat she's never there for me. And when she does answer it's always about her, always! She just doesn't care about me. Is this normal?