Seeing a dentist is the best option, don't won't, because you'll regret if you don't go, just like me.... I was nervous and I didn't pay attention to time, I had a cavity, and it kept getting bigger and bigger, which is NOT good, so later I went to the dentist after about three months and had to get those holes filled:/ but just go to make sure whats up with your teeth;)
Could be a variety of things, anything from cavities, swollen gums to a cracked tooth. If it's something that's been happening for a while, it wouldn't be a bad idea to see your dentist. If it gets worse, you could have a toothache at 3 am in the morning on a weekend when the dentist isn't in, speaking from experience, that's not good.