training but gaining weight?!?!

I used to be only a runner. I just started triathlons last year (if you can consider doing one try-a-tri a start). I noticed that before (when I only ran) that I'd lose weight when I started. Last year when I trained for my first event, I gained a little weight. This year (after a winter of doing almost nothing) it's happening again. Any ideas why? Maybe it's because swimming makes me hungry. Hm.