Thanks for your query.Based on the facts that you have posted it appears that you have
peeling off of the foreskin after taking antibiotics for 3 weeks for Prostatitis
One thing is sure that this is not due to antibiotics that you are taking .Please get your blood sugar levels tests done to rule out Diabetes
.This could be a fungal infection
that commonly develops in diabetic individuals.
In the mean while take anti fungal medications like Fluconozole orally with topical anti fungal jelly like Fluconozole for local application over foreskin for 5 days .
Observe proper personal hygiene by cleaning the genitals with warm water twice daily.