When will I see the results of swimming?

I am swimming Monday-Saturday for about 2 hours. I'm really trying to loose weight by eating low caloric foods like lean cuisine etc, i got into swimming eating about 940 calories at most and then I eat about 300 calories when I get home. I'm 5'5 and 140 and really want to loose 20 pounds this summer and tone up. But lately I've felt SO hungry and like I had nausea but I think I've been eating fine? Any tips? and when will I see the results of swimming?