Eating 3000 calories a day??

Lot of questions packed in there. I suggest you start at the beginning with the key question and work your way outward from there. The key question is: what is your daily burn rate for weight maintenance. According to TDEEcalculator.net, your burn rate, assuming you are Sedentary, is around 1800 calories per day. If you are lightly active, your burn rate would be 2050. Maybe you're between those two numbers, but in any event you are most likely in that range.

So to answer your specific question, if you eat 2000 calories, you'll probably about break even and not lose or gain much fat. You would have to create a calorie deficit from that 1800-2050 baseline to lose fat.

In truth you shouldn't feel hungry at all while eating 700-1000 calories over your maintenance level, and that hints that you might be eating the wrong stuff. It's possible to spend a lot of calories on junky, empty calories and refined carbs and not feel full, whereas protein, unrefined carbs, fats, etc., can be much more filling.

You might've screwed up your hunger and satiety signals with all the bouncing around from undereating to overeating (1000 calories is way, way too little food, and gaining 42 lbs in 4 months implies severe overeating). Reconditioning your body - and mind - to be adjusted to a proper day to day calorie level could take a while but is doable.

My recommendation would be to work through the MFP goals tool with a 1/2 lb per week goal and eat exactly how many calories it tells you to eat everyday, never less, never more, for at least a month or two, so that your body and mind get reoriented around consistent, proper amounts of food. That number will probably be around 1600-1700. I suspect when you get some time under your belt of consistent, mild calorie deficit eating, everything will readjust and you'll be fine. You might have to just be a little hungry at first - that isn't the end of the world, just be a little hungry. It won't kill you. What could kill you is continuing with the unhealthy cycling between severe undereating and severe overeating. Get past all that. Eat the # of cals that MFP tells you to eat for a 1/2 lb per week weight loss, no more no less, everyday.

But even before doing that, I would probably take 2 weeks and just eat an exact 2,000 calories per day with the intent of retraining my mind and body to take in the proper amount of food to maintain my weight. No extra snacking, no giving in to hunger, no undereating - just a clean, healthy 2,000 calories so you get reacclimated to what a break-even day worth of food really looks and feels like.

I maintained on around 2900 a day - female; 5’3”; 160lbs

I walk 3-4 miles most days at work; not including my workouts

154 pounds at 5'7" puts you in a normal BMI, so if you want to maintain this weight, you need not change anything.

But yes, if you are maintaining at 2500-3000, dropping calories to 2000-2500 will result in weight loss.