Courtney, Crocus has given you good advice. Maybe it is best not to go into details in public but I am wondering if this overdose was intentional or not. A lot rests on if it was done with the sure knowledge that she would be found by someone or not.regardless it is too much for you to manage on your own. Maybe mum needs a short spell in hospital to get proper treatment. Does she have a crisis team contact?
If so, they need to be made to understand it is unacceptable for you to try and deal with this on your own and without specialised help. They are a mental health crisis team and should be available when there is a crisis, not afterwards.
You cannot be responsible for your mum's actions, no matter how ill she is. By it's very nature, mental illness can often be a very selfish disease with the sufferer totally wrapped up in themselves.
I think you should have a word with your own GP too, you need some support while all this is going on, I seem to remember you have a brother too? Please get some help for yourself, you are important too.