Suggest Remedy For Itchy Red Cracks

Age 43, 149pds, 5'6". Yesterday, I felt a little itchy & it was red in the top of my butt crack (on both sides). Today there are 1-2" lumps on both sides, its very itchy & uncomfortable to sit. I'm highly allergic to poison "everything" & thought it could be that. My husband looked & said its not. I don't wear tight clothing, I wear cotton underwear & clean myself daily. Any idea what this can be? Thank you