I've gained a TON of wt. It is very uncomfortable. I lost 20 kind of fast, it didn't even show, and like she said 8 came back real fast too. My husband just lost 50 lbs in about 9 mos since he had a heart attack. He bought a calorie book at Walmart, it tells about fastfood, everything. Shocking. I figured that my lower cal lunch at Burger KIng was smart. Sm. cheeseburger, sm fries, sm shake - around 900 cals. Not good. Knowing that is very useful. Panda Express? OMG, everything is half fat cals. Check that out. How he did it was to measure or weigh everything. Amazing how small a portion is supposed to be. Counted his cals for every meal so he would know what he had left for the day. Shot for 400 cal/meal. Really had to cut down on meat portions, go to lean, and eats wild Salmon 3 x/wk. Lots of fruit and veg, especially carrots and cucumbers, very low cals.
You can do this too. You only have 20 to lose, and you're young. Get some exercise, my downfall, even if its walking faster than usual. A quick walk around the block before bed feels great. Good luck.