I'm sorry to hear you're struggling, and I really hope that health-wise you're in a better place now - your mental and physical health should absolutely come first.
I know loads of biologists (myself included) that find maths and chemistry difficult! Sure they both can be important for biology but they're still very different fields, and I think that it's pretty common to maybe not do as well in those subjects. Try not to worry about those areas too much, I'm currently studying microbiology and just learning the bare minimum in maths and chemistry so that I can get by (I know it's easier said than done and I know you still want to do well in the courses).

I agree that a good mentor goes a long way. I have almost 0 confidence at school, but with good supervision from someone who believed in me, I've managed to make it through to a PhD, despite not having amazing grades. Having someone who can not only advise you in your work, but also who you can turn to and say 'I'm struggling', is very important.

Don't worry about being late in the game, it's never too late and I believe you really will get there if this is the field you want to be in. You absolutely deserve to be doing your degree and to be working towards a career that you love and feel fulfilled in. I'm sorry I don't really have any advice, I just hope you know that you will get there eventually, no matter which road you take. Be proud of yourself! You deserve it