So I'm having issues with weight I've lost starting to creep back.

I was hoping to be able to lose a little more before the wedding or at the VERY least maintain.I am set up to start working with a trainer for 2-3x per week starting tonight......I have been known to work out about 3x per week so this isn't that different except I'm hoping to really work on adding resistance training and abs. The issue is whenever I seem to amp up my work out I put on weight!!!! It is so annoying since that is not the point!I wonder that I"m not eating enough calories??? I know from my past history that anything drastic just throws me off so I'm hesitant to cut out lots of carbs etc. So here is what I typically eat:Bfast: cherries or whole grain cereal with some skim milk and small piece of fruit (usually 1/2 banana or raisins), coffee with sugar free creamerLunch: sandwich (light bread 2 pieces with 2-3 pieces deli meat), and fruit, diet sodaDinner: varies....usually more protein than carb, but is maybe a stir fry (I use cooking spray), meat + veggie, salad, or a chicken fajita on a corn tortilla with some low fat cheese. After dinner: I might have berries and light cool whip.....or on weekends a small portion of a dessert I prepare for FI. It just varies....or I might have nothing at all. Recently 1 cup of coffee with some sugar free creamer too.**That is usually my structured meals. Sometimes I find myself snacking in between on things like chocolate, but what is odd is occationally I will find myself losing weight when I restrict less rather than more.So I'm wondering maybe I just need to add some calories somewhere to rev my metabolism? Maybe I need a post workout snack? I don't know! Suggestions please :-)