First reaction to allergy shot

Into approximately 6th week of allergy shot therapy.  Yesterday, around 1:30 p.m. rec'd injection and I immediately started itching at injection site on left arm.  It made a weal about the size of a dime.  Told it was ok.  It itched all evening, and still itches this morning.  The swelling went from size of a dime to size of a baseball.  At 6 p.m. I took black marker and made spot marks around it to see if it increased or decreased.  It increased.  I took Benadryl also, which seemed to help the itching.  No other problems but wondering now if I dare have the next round of shots.  I looked up reactions and it's not uncommon to have this happen but usually subsides in 4 to 8 hours.  I am well past 8 hours.

Advice?