Working out and gaining weight - Help!

I just started an exercise routine that I have been following for the past two months. I go to the gym 6 days a week for an hour. I mix weights and cardio. I alternate which areas of the body I concentrate on every time. My goal was to lose 15lbs and tone up but I have now gained almost 10. Can anyone tell me what I'm doing wrong or why I'm gaining? I realize muscle weighs more than fat but I still think I should be losing and not gaining. Help!