Hi,
If it’s not 
sexually transmitted disease then it can be – 
Acne , 
Fordyce spots -  which develop when skin's pores are  clogged with natural oil, called sebum, sweat, dead skin, it can also cause infection
Pearly penile papules - small, fleshy bumps that usually develop in gland penis in rows around the head of the penis.
 Skin tag – its normal , happens in age advances 
Lichen planus - 
Ingrown hair which is painful can leads to  infection , needs medical management 
Rough Masturbation/Sex
Pemphigus
If its sexually transmitted Disease (STD). 
It can be  
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