You can feel cavities...I've had 5! (i have no enamel on my teeth..Born without it so I get them easily) and boy oh boy do they hurt!
It starts out with your teeth being oddly sensetive to cold and hot things. Then it starts to hurt then it really starts to hurt. And if you dont get it fixed soon it can get underneath your tooth and into your gums and stuff and you have to get a root canal. Which hurts like crap...
But if its more then one tooth then its prolly just sensetive teeth...But if your worried you shouldnt wait. Go to the dentist...Because you dont want a root canal.
But then again, it may vary from person to person.