Hi OP,
Congrats on the pregnancy.
I don't want to piss on your chips but what you say about sticking to prepackaged foods because you know the calories and restricting to only calories sounds very much like what I do when I am in a restrictive phase. I was diagnosed with EDNOS after going to hospital with heart palpitations and breathlessness.
It turns out my electrolytes, urea, and potassium were worryingly low. 800 calories is not enough to live on. And honestly, your diet sounds much worse and much less varied than mine is when I restrict.
Please get help if you feel this getting out of control. Also, cook. You cannot really overeat on non-starchy, fresh veg, lean proteins and eggs. The calories if you miscount by a couple of grams would be negligible and you've a big enough buffer on less the 1200 calories a day to absorb that and still lose.