Overweight with constant farting?? kinda long but i need help!?

i have a 5 year old daughter that is having some issues. Since she was a baby she has had problems pooping. dont get me wrong, she still poops almost everyday but not like a normal person should. its usually hard and often she strains. she is also overweight. at 5 she weighs exaclty 100 lbs. Docs say she is overweight. She also farts constantly and un controllably. all day and everyday. I have taken her to the doc and they have tried dif methods of trying to get her bowels to move and each medicine doesnt really help much. deep down i think there is something wrong inside her tummy or something. she starts school this fall and want to try to get something solved before then but dont know where to start. any ideas of a starting point?