H.M.
You could have some of the food or the shell stuck under the gum. Popcorn kernels are really bad at doing this. I would suggest brushing it really well, swishing with water or mouthwash, flossing, and if you have a waterpik...that would be the best thing to use. It will flush the debris out. If it doesn't get better, then I would contact your dentist. You may need your teeth cleaned....gingivitis and/or periodontist could be occuring as well if it has been a while since having your teeth cleaned. Hope the area feels better soon.