I pulled a tick from behind my knee 3 days ago. So far I have not experienced any symptoms. Should I still be concerned about Lyme disease?

Ixodes scapularis. You do need to make sure it wasn't a deer tick. They are very small..compared to dog ticks for example. Do you still have the tick or did you discard it? If you have it, bring it to your PCP. f there's any question that it could be a deer tick, I would treat with doxycycline just to make sure.