Stomach aches daily in the afternoon

Okay Ever since June I have been getting stomach aches almost on a daily basis.  The pain is around my bellybutton and feels more toward the right side but i am not 100 percent sure on that.  The pain is not terrible but enough to stress me out about it.  I dont drink pop or anything and I try to eat somewhat healthy.  The pain usually starts around 4 or 5 pm and almost always stays with me till I go to bed.  My dr. gave me a medicine that worked at first but then stopped I cant think of the name it was like protozone or something like that.  Then he perscribed me nexium in the last week and that has not worked at all.  I dont know what to do it bothers me so much.  The current medicine I am on is risperdal 1 mg I take at night.  Then focalin xr 20 mg in the morning and then again in the afternoon.  Thanks for any help you can provide me.