Suspected brown recluse bite yesterday afternoon, been 21 hrs ago, about 10 minutes ago, sharp pain under armpit.....could it be related?

You like spiders! Anyway I can just interact directly? Brown recluse usually causes severe necrosis in the area of the bite. There is nothing to do for these bites unfortunately until weeks after the bite. The pain and necrosis all occur at the site of the bite. So if you were bit under the armpit, then yes, could be related. Otherwise, no.