What Causes Red Pimples In Groin Area?

Hi doctor, I am a 25 year old, 85kg male. Doctor I have these small red pimples on my groin area, since about 4~5 months ago. They are red at base with yellow tops, and some are joined together like they have a common base and have multiple heads. They started out on my groin and now have expanded to my right thigh. Initially they were hard with flat tops, but now they seem to be soft. They are not itchy, nor painful. Recently I started applying antiseptic liquid (Detol) on them, most of them disappeared leaving behind dark purple marks, but few grew again.
Doctor I live in Africa (for job) and I cant go back till my contract ends (4 months), and there is no hospital here. What can I do?
I am afraid I have some STD, I always have had protected sex, but I read that skin related STDs can be contacted even with protected sex. Please help me. I'd grateful to you for my life if you can prescribe some common cream or medicine to help me. Please try to understand there is no hospital for me for next four months.