What is this big painful spot near my butt crack?

Hi,

Please can any one tell me what this is.. It is on the side of my butt crack and is a big black spot that seems a bit yellow from the picture. I cannot see it as it is behind me and it is VERY painful. Not been doctors yet as embarrassed to get naked in front of them. They seem to reoccur in different locations but no where near as bad as the one I have got currently. I usually just have a shower and clean the area up and they disappear but why are they reoccurring in the first place? Not sure if a shower will make this one disappear but the spot is very soft to the touch. It definitely has yellow liquid or something inside it but do not want to pop it as not sure what will happen. :(

Accidentally posted the question in the women area before posting it here so it will show up in 2 discussions.

Thank You.