From what you have said, I understand that the painkillers are unable to ease your pain, and I assume that your pain is spontaneous ie not triggered by hot/cold? Does it get worse with biting though?
Your pain may be due to nerve involvement, possibly due to long term bacteria invasion from the decay you previously had, or the tooth may be cracked too. Although at times sensitivity after fillings is common, just that it is usually not as severe a presentation.
I personally think that your signs and symptoms points to the need of having a root canal treatment. You could consider getting it treated by a root canal specialist (Endodontist). Amongst my colleagues, their choices are Dr Timothy Sim from Simply Endo and Dr Lui Jeen Nee from National Dental Centre.
