My Husband And I Just Got Back From The Bahamas

My husband and I just got back from the Bahamas and he has an obvious bug bite behind his knee that is red, enflamed, has skin blisters around it and an obvious crater in the middle. We do no know what it was but we were out in the jungle as well as on the beach and he first noticed it the morning after. There was a black-red circular flat disc in the crater but I removed it with tweezers (it just looked like a dried blood clot, no obvious insect parts or anything). Since he first noticed it he's been experiencing vertigo, light-headedness, nausea, diarrhea, stuffy nose, scratchy throat, and just a general "unwell" feeling. The bite is not spreading or getting larger but it is nasty red, blistery, about the size of a quarter and very very itchy. Is it serious enough that he should he see a doctor or just keep treating at home with benadryl and antihistamine cream?