Gaining weight but I exercise daily?

I was always a pretty slim girl. Im 5'7 and currently weigh 144lbs, although a few weeks ago I was only 140lbs. I started swimming 6 days a week, and its very intense. Why am I gaining weight if Im working out more now? Any tips on how to lose this weight and maybe bring me down to 130lbs?
Gaining weight but I exercise daily?
Post Opinion