Why am i constant pain with my teeth?

It seems to be my filling on the bottom left of my mouth - I swear my dentist has not filled it properley. like when i brush my tongue over my teeth it has a hole in the filling (feels different compared to my other filling on the other side of my mouth) and i brush my teeth like 8 times a day i'm that paranoid about my teeth - i floss, use mouth wash, and the orabrush so to prevent anymore decay. But still i'm in such pain with that tooth. i don't have a bad diet i eat junk food on occasions like all people do but i don't live off of it like alot of people and i always brush my teeth straight after. Do you just think its the filling thats the problem, is it possible it's fell out without me realising?