Eleven month olds can respond to environmental
allergensAllergen
Positive reaction to allergen but an allergic response limited to the
eyelidsEyelid bump
Eyelid lift
Eyelid twitch would, while possible, be rather unusual. There are a number of other causes, infectious and mechanical for example, of eyelid swelling. The best advice I can give you is to seek consultation with a Pediatric Ophthamologist (eye specialist), who should quickly be able to diagnose the problem. Since the Benadryl doesn’t seem to be helping, you might want to ask the doctor who prescribed it if you could temporarily discontinue it, until your child is examined by the eye doctor.
Good luck