Your dog needs to be examined by a veterinarian. It does sound like an allergic reaction. Insect bites can cause swelling of the muzzle, lips, and around the eyes. Dogs typically become itchy. When they start having vomiting, diarrhea, weakness and collapse then they are having a severe reaction called anaphylactic shock. This is a life threatening emergency. Your dog needs to be evaluated then receive injectable Bendaryl and a steroid. You will follow up with oral Benadryl at home--the dose is 1 milligram per pound of body weight by mouth three times a day for 2 days. Do NOT use the Cold and Sinus variety--it needs to be plain Benadryl.
