Please Help. STD?

A few months ago I had an acne looking rash on my shoulders, it went away, but is now on my chest. As far as “down there”, it’s a disaster!!! I have no discharge it seems like- and the discharge I do have is milky white and very white. No smell however? Everything smells fine...This causes my vagina to be SUPER dry and very itchy! My scratching creates (I think this is the cause) of small fissure cut looking things down there. I have now realized that there is a red cleanly defined area of skin that looks super red in the areas it creases down there (if this makes sense). I thought it was a yeast infection but monistat, and then 2 yeast infection pills from doctor and still NO improvement! I’m so scared right now I’ve convinced myself I have HIV or something... I’m 17 and I have been wanting to go the doctor for so long but I’m so scared about how to explain this to my stepmom- and also, I’m scared of the results. I just want this to be gone and I have no idea what it could be. Please help