So, I've done the whole diet and healthy eating thing before, but I feel like last time I was getting much better results. (Unfortunately, I've gained back everything I lost last time!)

Its been a month, and other than water weight (which I dropped literally the day after I started) I haven't lost a pound. I count calories, so I was between 1000 and 1200 calories almost every day (sometimes slightly over, sometimes slightly under) and I was doing a really good job not cheating :/

So I guess my question is... anyone know what I was doing wrong? I have heard that not eating ENOUGH can cause you to not lose but... that seems like bull to me (lol). Is your metabolism slowing/"starvation mode"/whatever ACTUALLY a thing? I guess I'm just frustrated because the last time I was this weight and started dieting, I dropped something like 10lbs that first month

It's highly unlikely that you're not eating enough. You may be underestimating your calories. How do you measure? Do you weigh your food? What do you use to track? Are you doing any exercise? What kinds of food are you eating? Are you drinking enough water? etc. etc. etc....

I would use an app for what you should eat for awhile.i wasn't losing and then I started tracking and now I'm pretty good at chosing helathy things.

If you aren't losing despite counting calories, consider cleaning up what you're eating before tacking on more calories. Cut out white things; grain, sugar, etc. Add on an extra serving of veg at each meal, real veg, no corn, peas or beans.
If you totally clean up how you're eating and you still can't lose, consider bloodwork.
"Starvation mode" is and isn't a myth. Your body will hold onto weight, but only for a day or two. If it truly existed, anorexia wouldn't be a thing.
People lose on very low calorie diets, but they're typically under doctor supervision.
Like I said, clean up what you're eating, work on portion control and write down EVERYTHING. Then go from there.

sounds like you definitely aren't eating enough calories. you need to do some research into how many calories you need to be eating in order to lose. because even when i'm in weight loss i rarely eat under 1350 calories.

I haven't posted here at 3FC for a while but I just wanted to add my two cents since I went through something similar when I started on my journey

I agree with everyone who said that you may not be counting calories as much as you think. Even what I thought was 2tbspns of peanut butter when I started changing my eating habits turned out to be more like 4. Portions and amounts are deceiving.

But more likely I think you just have to be patient. It was ONLY a month. When I first started tracking calories at 223 pounds, the scale BARELY BUDGED after a month despite incontrovertible math which estimated I should be down 6-8 pounds. But I stuck to my math and then it started going down in whooshes.

I think there are a few things at play when you FIRST start eating less. First... you may be pooping less because you'll have less bulk. LOL! And all that "weight" is in part the weight of your unrealized eliminations. LOL! Sorry to get a little graphic.
Also, healthier food tends to actually be HEAVIER in weight (but not in calories!) because fruits 'n veggies have high water and fiber content than say... pizza or mac and cheese. One is HEAVIER in weight per unit of size but NOT in calories.
Also, I was drinking more water. While water certainly does not add more calories... It does add "weight". And quite a bit at that since 1 gallon of water weighs roughly 8 lbs.

Be patient! And be sure of your math! The REAL "weight" will go down. I promise if you just stick to the numbers. Don't get hung up on "weight" that simply hasn't been ousted yet or may be reintroduced but doesn't represent any caloric value and thus fat. Only time, catabolism of body fat, and peristalsis will win the day