Ok why have I gained weight?

I'm glad I'm not the only one. I've been doing weights and cardio and I've gained 5lbs in 2 weeks. I've started doing more cardio than weights, and eating slightly less though and I've lost about 2 lbs this week. I think some of it might have been water weight (due to my weight training). I don't know if that could be the case for you but I thought I'd just throw that out there.