I Have A Space Between Two Teeth Where Food Collects

I have a space between two teeth where food collects occasionally. My dentist did a filling to close up the space but it still has some issues. The other day I suddenly got a lump swell near the teeth. I flossed and swished with peroxide and it seemed better but the lump is still there. At first I thought it was an allergy to a shrimp salad but it's still there 3 days later. When should I be concerned?