Mystery red itchy bumps for 3.5 weeks. Spider bites?

[8945MariaG]

Three and a half weeks ago I had 6 extremely itchy welts appear on my bottom and lower back and one more on my ankle.  The first one appeared at 10 pm Sunday night and the last one appeared at 3:00pm the next day.  I happened to have a (non general practitioner) doctor's appointment that Monday morning and asked the doctor to take a look, he said he suspected shingles and wanted me to see my GP doctor and get tested.  I felt terrible that day, pounding headache, slightly sore throat, my blood pressure was 140/100 (normally my BP is low, it's rare for either number to be triple digits, much less both). That afternoon I went to my GP and more bumps had appeared by then and she said it wasn't shingles and thought it was a contact dermatitis or bug bites and gave me a cortisone shot.  Since then the welts will seem to calm down and look like they are going, but then will take turns randomly flaring up for a few days, but never in new spots.  They get raised, hard, red, sometimes blistery, and always super itchy.  Also, not sure if it is a coincidence but I had headaches for the first two weeks (which is unheard of for me), been sleeping terribly, and have had diarrhea daily.  Other than this I am a healthy 30+ female with no significant health issues.  Any ideas what is going on?  Would bug bites linger for this long?