small boil on the penis

Hi,
I'm a 20 year old student studying medicine in china. I'm from sri-lanka. i'm an obese person and i have no luck in a relationship with a girl in my batch. On December 2011 i had unprotected sex with an escort girl for around 10 minutes. i was so worried the next day about the unprotected sex. When i came back to sri-lanka after 6 weeks i had an HIV test and it was negative. when i came back in February for the 2nd semester i had safe sex (wearing a condom) twice with 2 escort girls. however before wearing a condom one girl gave me a small blowjob.

My problem is that there is a skin colour/ light pinkish boil on the tip of my foreskin. i doesn't hurt. its about 6mm in diameter. I haven't shown this to a doctor and i'm embarrassed to do so. The boil appeared a few days after my unprotected sex. Recently i noticed that there is a second very tiny similar colour boil roughly about 2mm on the penis shaft. Also i have the habit of masturbation but i guess its a STD. What should i do? Also should i do another screening for HIV? If it is necessary i can email a picture of the boil if it helps to confirm the diagnosis. I'm really worried about the boil and my mistake of having sex. I have been a virgin till i broke it last December and now i blame myself for getting a boil. Also eventhough i got a negative HIV result, i'm scared that i might have it.

Please help me with my situation and offer me any possible Advice,

Thanking You,
Best Regards