What Causes Growth Of Bumps On The Back Of The Shaft?

Hello, excuse any typos but i am 20 years of age and i noticed a group of small lightly red bumps at the back of my shaft were my pubic hair grow. It is only a few, between 5 and 8, one is fairly larger than the rest, but overall small. Now I have eczema and I do shave often But i have had eczema for years and when it came on my penis it cleared away really quickly, i know that these are not shaving bumps they simply do not look like it. I was thinking a pimple because i have really bad acne but that is only on my face. I have noticed in my sex life, if i do not use a condom, after sex if i did not take a bath my penis would itch. it never got server and bumped up badly. but when it did i treated it with hydrocortisone 2.5%..i had sex a little of 2 months ago with out a condom and i noticed that my penis itches after. It was not anything new. but i did have a lot of sex for two days straight with out a condom. the itch did not increase. it really came and went away. until i took a shower. but i did notice some bumps and since they did not itch i left them alone. but now months later there are not as many bumps. there never were that many. but i just want them gone. and i am scared i might have an std. i treated it with hydrocortisone 1% i have no 2.5% and the 1% was over the counter. any advice?