It could be hypothyroid. When in doubt, check it out
A thyroid test will give you peace of mind, if nothing else.
While saying that, I had the same symptoms you did: initially, it was VERY tough for me to lose weight. I ate 1,200-1,500 calories a day, exercised like a fiend, was not in bad shape considering my size, struggled a lot with acne as a teen (I only break out during the time of month now, though) and therefore am still self conscious about my skin, and have been depressed on and off since I was 14. I am much better now, though - since my depression is primarily situational (I believe I have a slight chemical imbalance, but it is controlled without medication), I am able to fight it by focusing my energy on positive things and moving towards achieving goals that are important to me.
I've been tested for hypothyroid. Funnily enough, I've been tested for
hyperthyroid, too (post weight loss, long story) - yes, I've had the TSH test done twice
My thyroid is perfectly normal.
Perhaps you just need to switch up your exercise regime (try something new, push yourself harder, go for longer, etc) or temporarily
increase your calories for a few days.
PCOS could also be a possibility. That or insulin resistance. Insulin resistance is a very common problem for those who are overweight and obese, ironically makes it even harder to lose weight, and luckily goes away for most people once they *do* lose weight.