What are possible reasons that could be preventing me from losing weight?

I stand at 5 feet and 6 inches and weigh 150 pounds. Two months ago, I was on the keto diet for a month. I lost 3 pounds, despite the fact that I was regularly calculating my macros and making sure I strictly followed the diet rules. I regained the weight I’d lost shortly. When this attempt didn’t work, I tried clean eating, eating 1200 calories per day, and exercising 5 times a week, with 2 days for rest. I’ve been following this for a month and have not lost anything and at this point this is just seeming ridiculous to me. What could be preventing me from losing weight?