Hi.. Can understand your concern.. As per your complain it seems that you may have drug resistance to amoxicillin due to which it is not able to reduce your infection or in case of severe infection along with amoxicillin there is a need to add another drug like clavulanic acid to increase the potency of antibiotic and to kick of the infection faster. It seems when your root canal treatment was done the final filling when done you must have had active infection present below the root tips of infected tooth and due to which after the tooth got sealed with the filling the persistant infection must have led to pus formation and as the pus cannot come out it creates pressure on the nerve tissue in that area causing pain.. The other thing is that amoxicillin 250 mg is a lesser dose for adults and needs 500 mg three times a day in case of dental infections. I would suggest you to consult an ENDODONTIST and get clinical examination and IOPAR (x ray ) done so that he can rule out the cause of pain which seems most probably recurring infection or persistant infection. If required he will remove the root canal filling and put calcium hydroxide dressing into the canals to aid in reducing infection and relieve pain and prescribe you higher antibiotics like augmentin to reduce the infection and discomfort due to it. Painkillers will also be advise to relieve pain. Hope you get well soon.. Thanks and regard.. Dr.Honey Nandwani Arora.