Developed Blisters On Penis That Goes And Comes Especially A Day After Sex Or Masturbation. What It Could Be?

I have developed blisters on my penis that goes and comes especially a day after sex or masturbation. These blisters often turns into a sore then heals normally like a cut. They tend to appear more on the foreskin of the penis but they can also appear on the glans penis as well. I have tried several creams but only hydrocortisone seems to work. These blisters responds rapidly to hydrocortisone treatment. So much that they doesn t develop into a sore but just seem to decline. Doc can u tell me what I have? I am thinking psoriasis since viral, fungal and bacterial infection doesn t respond to hydrocortisone treatment?