What is wrong with my tooth?!

What is wrong with my tooth?

Ive had a toothache for about 3 weeks. By toothache I mean a constant pain which I was taking painkillers every 6 hours for.

I got to see the dentist after a week and a half and he took out a filling that was in and i was going back a week later t o have the proper one put in. My tooth still aches

Went back and he's taken out the nerve I think and it was fine but now it's aching again (not as bad though). My tongue also feels dry down the side the tooth is on

2 months ago
I have to go back in August but I think thats for a check up and to get a proper filling put in

You haven't been told the full story. This dentist is hiding something from you that he has a duty to tell you. Your tooth is probably cracked and that is causing pain as infection is getting in. Go to another dentist, dont reveal who the first dentist is, or what he did. Just tell him your complaints of pain and ask him what is causing the pain. There is much more here than a bad or improperly installed filling. In taking the nerve out, he did a root canal. You should have been advised of this with specificity and not just left to think thats what he did.
If the dentist is honest, you will then know truth. But if you find out he wasn't, that the tooth was cracked and he never told you about it, and you had to go to another dentist to learn the truth, then get a lawyer after that and sue.