What Causes Swelling And Rashes On The Foreskin?

Hi, I am 25 yrs old male. Married since dec 2010. started living with my since a week. my wife is not that tight to penetrate, but now a days every time we had sex my foreskin gets swollen up and red rashes come on penis head. urine test of both of us is normal. i have taken cyproheptadine hydrochloride tab 4mg and co-trimoxazole tab 480 mg bd for 5 days and also applied pure glyserine locally. today i did masturbation, just to check. but it it didnt help. i'm in great pain plz help.