Bloated belly problem?

i always have a bloated belly, well often i do. Its just annoying me now 2 people have asked if i am pregnant but i have had my period 2 weeks ago and been on the pill for over a year. I took a test just out of curiousity and it was negative. I have started dieting a week ago and it shouldnt make me worse should help me lose weight, im not overweight im average just want to lose bit of the puppy fat. I go for a crap reguarly but i dont know what causes this bloated belly thing, i dont eat break and i only have rice/pasta occasionaly or weekends, anyone got any other reason i may be getting this?