I've gained 8 kgs in 3 mths and has yet to shed them after nearly a year!?

Well, i've lived my life as a couch potato for 3 mths and gained 8kgs just like that. Problem is, i've been exercising (cardio and toning exercises) regularly over the past (nearly) year and nothing seemed to be working at all. Moreover, i realised that I'm not perspiring as much as how i would use to when i'm doing the exact same exercises. What's happening to me? Oh, and apart from the sudden weight gain, i'm also experiencing horrible skin. Dry, peeling and with frequent pimple outbreak. is it hormones?