Small red sore lines, appeared between my ass cheeks. What could they be?

I have noticed sore red lines, about 4 of them appear between my asscheeks, not on the anus though. They are very sore almost a stinging pain. I noticed they were just there when I woke up in the morning. They look almost like a vein under the skin, squiggly in shape. They're definite lines not pimples or bumps. 

Side note: I haven't been sexually active recently so I doubt this is a STD but something else perhaps? if  knows what this is or the cause of it I'd really be greatful for a reply. If it continues to get worse I'll see a doctor but it's rather embarrassing :/ 

thank you for reading! Hope for an answer