What Causes A Neon Green Residue On My Underwear?

Hi, I'm 21 and still a virgin, I recently started to get neon green residue on the left side of my underwear, there is not smell but also same place (between inner thigh and left side of my vigina ) I noticed it was red And sore it also burns and itches! The green residue always appears on the left side of the underwear. I need to know what it is? Is it serious? Will I have it forever even after treated?