Was bit by a bug about 2 months ago while taking my dog outside. Not your normal mosquito bite as this actually felt like a sharp little pinch. I swatted at the area but never saw a bug/spider/tick. However just a few weeks ago this "bullseye" rash popped up on the same spot behind my knee. I had bloodwork done for lymes disease which came back negative today. Any idea what bug may leave a similar bite mark? Picture not the greatest but it's looked a lot more defined the past few weeks
Unfortunately, it is nearly impossible to tell from a bite mark alone what critter may have been responsible. It is unlikely that a tick was responsible for yours, as (1) tick bites usually are painless, and (2) once attached, a tick stays in place until fully engorged, usually takes several days.
All that aside, as your 'bite' does resemble signs of some Lyme disease rash (see https://www.mayoclinic.org/diseases-conditions/lyme-disease/multimedia/lyme-disease-rash/img-20006687), you might request a second test just for peace of mind.