I feel the best thing for you to do is talk to someone who you trust and totally be honest with them you dont have to feel so alone through this and you are being very brave if you do. Having depression is bad enough let alone thinking you may have bi-polar you need to have it diagnosed by a doctor first and then maybe you could tell the doctor about your mother.
We all have felt alone at one time or another in our lives but you are only 15 and this is way too much for you to handle by yourself.
I wish you the best for whatever decision you make but dont ever think you are alone.
warm regards scooby.