pain 1 month after filling

I got 3 fillings exactly 4 weeks ago.  One is perfectly fine.  One is really sensitive to cold things.  The third filling has had several issues: (1) it wasn't shaped properly and I couldn't chew on that side for 2 weeks, my dentist filed it down and now it's improved, but (2) since she filed it down, the tooth is so sensitive to cold that even a room temperature banana or room temp water feels like I'm holding an ice cube on my teeth.

I've gone back three times since having the fillings, and today was the most recent.  She told me a flouride treatment would help (so far no improvement from it), and also made me pay $30 for "GC MI Paste Plus" that I'm supposed to put on my teeth every night.  

Is this normal?  I feel angry that I've had to go back 3 times since the fillings and I still can't eat or drink on the left side of my mouth!  I've had cavities before (I'm 26) and nothing like this has ever happened.  What is wrong?  I can't go another 4 weeks not eating on the left side of my mouth...

[Jerome Tsang, DDS]

How long does the sensitivity last?  It may need a root canal.  If the symptoms don't indicate a root canal, replacing the filling with another one may solve the problem.