If melatonin let's the brain know it's time to go to sleep, what let's the brain know it's time to wake up?

This is a major issue for me, I find it very difficult to wake up. It takes hours, sometimes the whole day of trying to wake up. Any advice?
Edit: "lets", not "let's". But I was half asleep and now can't edit the title. It's really bothering me though.
Edit 2: Thanks all. Unfortunately my mom is not an option anymore so I'll look at all your other suggestions. Having been dealing with this for a while now, it really is incredible how little we know about sleep and hypersomnia in its many representations. Any future doctors out there looking for a field to specialize in, here's an intriguing one. And if you need a test patient... lmk.