Can I Use Erythromycin Solution For Blackhead On My Groin?

4 weeks ago, I had a bump in groin, pimple like then there s a black head in it similar to ingrown hair went to OB gyne and had this removed, I was given 1 week of doxycline. Apparently, a week after there s another blackhead adjacent to the first one which causes wider lump when touching this. I went to derma and she said that it s a build up of pus that wouldn t come out. It s no longer painful dont have other symptoms. Currently, I m just using hot compress. Question is why is it more apparent when standing rather than lying down? Can I use erythromycin solution in it, the one that im using in my face? Should I still take anti inflammatory to subside? I m thinking this might be acne inversa, hidradenitis suppurativa. Thank you for your help