Hi,
Since you had an unprotected sex.
Need to do investigation regarding STI
The common cause for your issue is
1. Herpes - Genital warts (HPV) can be diagnosed by the presence of very painful blisters, sallow ulcers or red base. There are treatment options for 
genital herpes, but there is no cure. As to the treatment, it is based on relieving basic symptoms, early healing as well as the decrease of symptoms duration.
2. If it’s not painful - Syphilis, diagnosed by blisters appear as the first symptoms of 
primary syphilis. They usually disappear on their own with time, but remains in the body. First blisters on penis appear, important to 
seek medical help.
3. 
Molluscum contagiosum - Small, painless bumps.
4. Yeast Infection - It causes blisters, redness, itching and swelling. Blisters are usually white-colour and thick.
Hope I have answered your query. Let me know if I can assist you further.
Regards,
Dr. S.R.Raveendran, 
Sexologist