It sounds like an infected sweat gland, based on personal experience. I have had this once or twice and it's a painful experience. Usually I have found that after a hot shower or bath, it will soften the skin and allow you to squeeze it with results. I will warn you that this is EXTREMELY PAINFUL; HOWEVER.......IF you're able to get it rupture, it will go down. Squeeze from the bottom and keep squeezing until you feel the majority of the fluid is drained. Going to the doctor is also an option which you'll probably get antibiotics and they may even drain the fluid as well.