Hello
Thanks for posting your query at DoctorSpring.com
I can understand your concern.
This seems to be a drug rash or it could be urticaria which could be caused due to either food, medications , dust allergy etc.
I would recommend that you visit your doctor as soon as possible, you can go to the er. It would be best to let the doctor examine you completely to check for any sores in the mouth, nose, genitals etc.
They might need to give you an injection to bring the rash under control. Antihistamine like Allegra would be useful till the time you can go to the er.
Regarding which drug might have caused the rash, usually a newly introduced drug or a pain killer, antibiotics are commonly known to cause a rash.
It would be best if your doctor was to review your medications.
Please let me know if you have any queries.
Regards