For 3 weeks now I have been getting bad stomach aches, gas pains, & cramping every day. What could this be? I have also had diarrhea a few times.

See below. There are alot of different things that can cause that from a viral infection, to a viral infection complicated by lactose intolerance, or even other conditions. If it persists, seek medical attention for a definitive diagnosis.
See your doctor. With theses symptoms, its best to see your doctor. He/she can listen to you and do an examination to find out whats going on.