hello It seems like a sebaceous cyst
which is infected from your description.
Let me explain what do I mean, their are glands(bunch of cells modified to do certain things) called sebaceous glands which secrete the sweat and an oily substance called sebum, they have an opening at one end and closed at other like a bottle normally it can get the production out from the opening but due to one or other reason the opening is closed/sealed and hence the production of sweat / sebum can't come out so it starts building up and it seems like a bump still at this time it will be painless, but slowly it might get infected and the infection makes it painful which is present in your case.
you need to consult your doctor whom you are comfortable with , I guess a lady doctor! right?
here is they most likely do
1) will take a visual inspection
2) prescribe some antibiotic and pain medication
3) if nothing works they need to make a small cut to drain the pus and collected sebum , may not need to make even a cut some cases they can just put a needle and drain out the stuff.
Any thing you do at home will make it worst and nothing except above mentioned steps works in such cases, PLEASE help your self, if you can speak u can make a print out and hand it to the treating doctor but its important to get an medical attention before it gets any more worst.
Hope it helps, Thanks.