How can i stop these terrible stomach aches?

im 13,girl, and i get extremly bad stomach aches! and no no its not menstural cramps it happens wayy to often! im soo sick of it! i guess u could say i have a bad diet, i do eat alot of greasy food every night and breakfast i eat mcdonalds i know its not healthy but i tried eating other foods but other food is totally disgusting! i cant believe people could eat other stuff because mcdonalds the food is good but regualar food is yuck nothing plain bland and doesnt fill my stomache also i dont drink water because water taste bad :/ any other suggestions besides changing my diet to make my stomach stop hurting?!?! (the stomach ache is everyday or sometimes i m lucky and get it everyother day)