It seems that the whole problem started after you were given immediate dentures. The first thing i would suggest you to get an X ray done as among all the probabilities there are chances of sharp bony spicules that might be causing you trouble even if you take off your dentures. You might require reshaping of the alveolar bone.
Another cause of pain can be ill fitting dentures with rough surface. You should get your denture checked by the dentist that did your treatment. Rather than continuously reshaping your old denture get a new set of denture. If cost is the problem than you can visit a dental school where it can be done as reduced price or you can also seek the help of CARE CREDIT.
Till that time, do warm saling gargels (it acts as an antibiotic) and apply ice packs (it will reduce swelling)...For more info about dentures and problems related to it you can visit....http://www.identalhub.com/articlecategory-dentures-50.aspx