Tbh there isnt much to go on what it could be i only have a few ideas, Its obviously some kind of infection, as to the nature of the infection if go see your GP, My first guess would be a staph infection. it could be affecting the second skin layer, which would explain why antibiotic cream your applying isn't working.
See your GP, you can request to see a female GP at your practise, I wouldnt be ashamed, they deal with things like this all the time, (treatment will probably be oral antibiotics)
Taking your age into consideration though it could also be acne. Sometimes spots can develop in strange areas due to the increases in hormones. Try acney cream see if that helps, if not see your doctor.
A sore fire way of knowing which it is is when it "Opens" does it look like a sore?.
Things like this can be embarrising at first but remember Doctors and GP's have been doing there job for years, they have seen everything you could possibly show them.
Good look and i hope i helped :)
Hun, I think you should go to the doctor. In my appion you should have gone a long time ago. Truthfully I dont think anyone on here will know what it really is, the best thing you can do for YOUR health is to go to the emergancy room asap!!!
Please keep in contact and let us know how everything is going ok.
Sencerally, Dida21