Does my Mum need help?

It certainly sounds as if her antidepressants are not as effective as they could be. This can easily be rectified by either an increase in the dose or a change of medication. She quite possibly could be experiencing other mental health issues that are not wholly treatable by antidepressants. As a child, discussing this with your Mum will not be easy, but as it is obviously having a negative impact on your life, something needs to be done. Perhaps you can discuss it with another adult family member.