don't feel bad about not weighing or anything like that. I didn't weigh during weight loss and I rarely do now. The only reason I actually
do weigh anything now is because we have a food scale--the one I bought my father. I get too obsessive otherwise.
If you've been estimating wrong, so what? At least you can change things if you want. As others said you have a bit more leeway than someone who only wants to lose 20lbs, but going under 1200 is still very low.
There's nothing wrong with actually eating 1200 calories for a while and seeing what happens. I know it's scary changing things though! But still if you're eating 850-900 it is no big deal to get up to 1200. A handful of nuts, slightly more at each meal, etc.
My hunger signals are forever borked as well it seems. I also need to eat on a schedule or I'll not eat enough. I tried eating just when I was hungry for a while and that's what got me down to 115 in the first place (I really wanted to stop at around 120)! I see all of these websites just advising people to "listen to their hunger signals" well that doesn't always work for some of us! Eating when I'm bored got me into this mess in the first place...
Just be careful. If what you're doing works then that's great but you also want to do it safely

I would really hate to find out that something happened to you because you went so low, but then again I wouldn't want you to get frustrated because you don't lose on a higher amount! Just be careful, be safe, and try to be as healthy as possible.