Losing or gaining weight? confused?

ok, so this is something i dont quite understand about weightloss. i want to get rid of these thighs that i have but whenever i go running, or jogging at 5mph for 1 or 2 hours i end up gaining weight somehow? i know my thighs are getting thinner because i measure myself with measuring tape but why am i gaining weight? i dont have any muscle at all and i'm gaining weight. i'm getting very unmotivated to do ANY exercise if i'm just going to end up gaining weight instead of losing it. I also eat healthy at 1200 calories per day and drink water. how am i gaining weight when there is no muscle? so this is how it goes i end up losing 2 pounds, then gaining 2 pounds, then losing it. it keeps repeating!?!?! can anyone tell me what i am doing wrong? i never get sore because i stretch before, could that be a problem?