K.K.
I've had this happen to me before - not with a filling for a cavity, but with a fake tooth - er, half fake. When I was in jr. high I got hit with a tennis racket and it knocked out the bottom half of my front tooth. There was something they attached to my remaining (healthy) tooth to make it even.
The first time it was fixed it looked sloppy and sure enough, a year later, it fell off. The second time I got it fixed, the dentist was like, "Oh who ever did this the first time was really sloppy about it or didn't know what they were doing!" Looks at my chart, and it was him....
Yeah, so the first filling was probably done half-a** (or by someone inexperienced) and thats why it still hurts. My dentist told me that a cavity should not hurt a week after it's been filled - and if it DOES hurt, either something is awry with the filling or the cavity is worse than what was seen on the x-ray. I was teetering between a root canal or a large filling when I was told this - and the filling worked.
The only reason I would consider having the same dentist re-doing it is so that you can get it fixed right at a reduced cost or free. When my dentist realized he was the one that did the botched job on my front tooth before, he didn't charge the second time. This was a dentist in Brooklyn Park about 10 yrs ago so unfortunately I don't remember his name. Either way, after that, I switched dentists and haven't had a problem with the front tooth since. Now I use Metro Dental and haven't had problems. I specifically go to the downtown Minneapolis location - but I would imagine locations would be the same.
Good luck! And congrats on making it so far without a cavity - pregnancy wrecked havoc on my teeth so I'm infinitely jealous!