Is my hamster ok? Does it have wet tail?

My boyfriend got me my new hamster on Valentines Day which was 6 days ago. Since yesterday he has had diarrhea. He is still running around on his wheel, drinking and eating normally. If I go and get him wet tail medicine will he get sick if he doesn't actually have it and just has a stomach ache? Please someone help I love the little guy and don't want him to be sick or die.