Every Few Days, Immediately After Eating, (sometimes During) My Lips

Every few days, immediately after eating, (sometimes during) my lips get really swollen on the inside. Sometimes it's mostly the top lip, and sometimes the mostly bottom. The symptoms last for several hours and Benadryl doesn't seem to do much to alleviate it. It's never my tongue or my throat, only one or both lips on the inside of my mouth. i'm not aware of having any food allergies and it doesn't seem to matter what I eat.