Without actually knowing what it looks like, my guess would be that the 'pimple' is most likely a boil (infection in an oil gland or hair follicle caused by bacteria). Use a warm compress to try and help bring the pustule to form a head and drain. And keep the area as clean as possible to avoid spreading the infection. It is usually not recommended that you treat yourself with antibiotics especially when you are not sure what the actual diagnosis is. However, a 5-10 day course of
cephalexin or dicloxacillin is the usual treatment if oral antibiotics are required. If it doesn't seem to be getting better though (it takes about 1-2 weeks for it to heal properly) or you develop chills, fever, swollen lymph nodes, then see your doctor.
ta