How to stop over-eating?

I frequently don't have much of an appetite, but I think that I should eat anyways, so when I do, I'll feel like I've eaten a lot. Or aside from that, I don't feel good about my body. so I'll try to restrict my food intake, and I overthink it and that stresses me out, but when I'm focused I can manage to control it for a few days until I think "screw it, I'm gonna try not caring" then I end up eating, then thinking if I already messed up then I should eat more to punish myself, then I end up feeling even worse about myself. Which leads me to try to eat less again, because I want to be thin. I feel like I'm just gonna put on a lot of weight and it makes me feel really bad.

I just want to stop over-thinking it and manage to eat for my appetite without it being so stressful and frustrating.