I don’t know what to do...

I’ve been feeling extremely depressed over the past year and recently have come close to cutting myself. I haven’t told anyone because I feel like I can’t tell my mum. She’s a single parent and my brother has had severe depression over the past three years so she spends all her time dealing with him when she’s not working. I don’t want to give her an extra burden but I’m not sure I can go on much longer feeling like this. I don’t know what to do...