Thanks for the query,
You have developed an allergic reaction
Any change in brand of same drug can also cause allergy.
Apply a mild steroid
lotion like desonide
Also take an antihistamine tablet.
This will give you some relief.
Try stopping the medication for few days and try for a different brand.
Please meet a dermatologist
for exact diagnosis.
Let me know if you have any other doubt.
you can ask a direct question to me on this forum, following the below link.
Wishing you a good health.