Please Help - Feeling Helpless with Desires

Assalamu alaykum. I'm a teenage guy and I've been struggling with strong sexual urges. I haven't watched pornography, but I still end up masturbating and feel really guilty about it. I want to explain what's been happening so it's clear. This year my body changed and my desires increased, so I tried to fast more during the summer and be mindful. But recently a big problem developed. I go to bed tired and fall asleep, then wake up about an hour later with overwhelming urges. Most of the time I'm half-asleep and end up touching myself and ejaculating. I used to have ordinary wet dreams and didn't worry about them, but now it feels different - like I'm more awake and giving in, and afterward I feel awful and guilty. It only seems to happen when I'm very tired, about an hour after falling asleep, which makes it really hard to resist. When I'm fully awake and in control, I would never do this, but in that half-asleep state I feel powerless. I hate that it keeps happening and I want it to stop. Any advice from fellow Muslims on how to handle this? Practical tips to avoid falling into that half-asleep state, ways to strengthen willpower, dua, or routines that helped you would be really appreciated. Jazāk Allāhu khayran.