Dissertion and scheduling anxiety

I'm a student on my senior year of university, and all I have left to finish is my end of degree dissertation, due for mid December.

The fact that I have been barely able to progress it because I don't know where to start/that thing I just wrote makes no sense/time passed with the blink of an eye/researching is like a bottomless pit hasn't helped my situation, on top of being constantly doubting myself and having paralysing anxiety.

I have tried many times to make a schedule and get used to it, but it's no use, and putting self-imposed deadlines didn't do the trick either. For many different reasons (these being some of them), I have the slight suspicion that I might have ADHD too, so I don't know how to keep myself productive without having to belittle every step.

What could I do?