Pain when pressing right side of my stomach and when i suck my stomach in. what could this be?

Many things: My first thoughts are bowel function: sluggishness of colon leading to constipation or motility disorders of the bowel (improper function of the smooth muscle in the colon wall). Your liver is in the right upper abdomen (your stomach is upper left) and, if inflamed, could be tender when you press, but I don't think "sucking it in" would cause discomfort. Only medical eval/testing can sort it out