Hi Ive Been Experiencing A Small Bump Under The Skin

Hi ive been experiencing a small bump under the skin of my buttocks right at the bottom of my tailbone for about 3 months now and within the last 5 days of having this its now turned into a huge pimple like bump that keeps refilling with puss and has a bad odor. The color is a reddish orange and it hurts all around it! Sore to touch, or lay on my back or sore to sit straight without having my body titled on one side and standing hurts if done for too long! Please help I don't have insurance and not sure what to do if this is something OTC or should be seen by a Dr? If I can treat at home what should I do?