Can you get fillings in cavities?

When I was younger I had a filling. Earlier this year I had it drilled out and replaced with a new one. Nut noe, my tooth id throbbing, and it is difficult to to eat on it. The gums around it are senstive also. On the inside of my mouth behind the tooth there is a whole of some sorts, that appeared when my tooth started hurtung. I have a dentist appointment set up but it's not for a couple months. Should i go in sooner? And is it possible that I have a cavity under my filling or something like that?!?!