infection in gums following a root canal

i had a root canal a year ago in my upper back tooth, it is still painful but not unbearable i have been back to the dentist 4 times regarding this tooth and reqused x-rays to see if there was a 4th root but he said there wasnt. he said he cant find anything wrong with my tooth and there is nothing he can do and i need to either live with it or remove the tooth i am afrad to get it out as my root when filled was 25mm long. i also have had problems with my jaw after the root canal it keeps clicking and i am under a different dr for that.

this week my cheek swelled up and i had very bad pain i couldnt even close my teeth together or touch my teeth all the teeth on the same upper side of my mouth were affected about 5 teeth. went to the dentist he said the tooth next to the one just mentioned above now needs a root canal and i have a infection above my teeth - given antibotics- 7 day course metronidazole 600mgs a day- i am now on the 6th day- pain a little better but still bad there is a lump in my cheek that hurts and i now have an absess (abscess) above the tooth effected that wasnt there before  just came up today,and a numb feeling in my cheek and gums in some areas and pain in others

my question is

-is this all steming from the first bad tooth?
-why have i now got an absess (abscess) after taking antibotics?
-do i need to go back to the dentist for more antibotics?
-am i doing something wrong to cause all these root canals? i brush twice a day-use mouth wash-and floss
-my wisdom teeth are also coming through-could this be contributing to the problem?
-is the problem with my jaw connected?
-would it be better just to have the tooth out?