There is this painful spot between two molars. it only hurts when i brush or water floss. when i eat and such it doesn't hurt. is this a cavity?

Possible: It is impossible to tell you if this is a cavity or if this is a problem with your gum tissue or something else. It may be a cavity.The only way to find out and to make it feel better is to see a dentist. It will not get better by itself.

Pain: Yes this could be a new cavity or a cracked filling that is causing decay. Pain is a sign that there is a problem that needs addressing so see your dentist asap.

Decay?: Get into a dental office and have the area checked with an x-ray and exam. If it is decay or a crack, better to get it fixed now.