Ulcers. Finished Regimen. Had Yeast Infection. Is Itchiness Due To Mosquitoes?

I was taking antibiotics for ulcers and finished the regimen on Monday. The very next day I was feeling symptoms of a yeast infection . I ALWAYS get yeast infections when I take them so I was prepared. I took monistat 1 day on Friday morning. I have taken this exact kind before so I wasn t worried. Friday night I broke out in hives on my legs around 11 at night . I took a Benadryl and went to bed. I woke up with ZERO whelps or hives. Saturday around 5 I started feeling itchy on my wrists - I assumed it was Mosquitos . By 9 at nightI was really irritated by the itch so I took some more Benadryl. By 10:30 my wrists, knees, several fingers and elbows looked like massive bubbles. I went to the ER and they couldn t figure out why I was having an allergic reaction or why I was only swelling in the places I was swelling . They told me to take Benadryl round the clock and gave me a steroid shot. What could have possibly caused this reaction . I have NEVER been allergy to anything before and the doctor said I had to have touched an oil or chemical I m allergic too... Any ideas ?