My Last Tooth On The Upper Jaw Was Painful When

My last tooth on the upper jaw was painful when the brush touches it.I went to dentist however since I had to leave the country Immediately I took my self to dentist late.He told me the decay was close to the nerve.Hence it is better to take it off since firstly there is less space to work on it and moreover the last teeth is just an addition even if it is removed you can bite and chew food.I was reluctant to remove it hence he did root canal to it in 1 sitting.It should have been done in 2days at least.How ever since I was in a hurry and leaving the he said he will do so in one sitting.He did it was too difficult to access by tooth they called it some. 8oclock something like that.After traveling in a day I started to get pain.Didn't know what to do.After 3days pain went.Its been many months 6 months.Now I get pain when I bite the last teeth this started immediately after I bit my inside of my cheeks and it is painful 5days passed after it still both are painful.I don't know what to do.Help