Dry skin? Chaffing? Rash?

Sabrina • 19&chocolate
Idk what this is but I wanna know remedies to get rid of it fast! The pictures shown below were taken 26/12/16 and has expanded since then. 
It's waxy-looking, dark and discolored, flaky-looking when dry. It looks like the skin of a rhino or elephant with all them wrinkles. 
Could this be dehydration from long hot showers? Thighs rubbing against each other? - although I have thin thighs and a slight gap. What's the cause?  
Just like 2 days ago for the first time and last time it began itching me while in the shower so I did for 2-3 mins. I think that made it worse. Please help! 
& No it's not std-related, never had sex nor have I had any sexual contact(o-ral) in this area since late August. & I wear VS panties. 
Left side:
Right side:
Update: I have genital psoriasis. It's a skin disease. Basically my skin cells multiply faster than normal in some areas. There's nothing I can do about it, I'll have flare ups at any given moment for the rest of my life there's no known cure or cause. They say if you have flexural/inverse psoriasis you're likely to have it other place like underarms or scalp, I don't though. It so happens to very common but in white people.... There are many types of psoriasis and they look different. I've been treating it with tea tree oil for a few days now and it's been getting smaller. It only was itching that one time. After a while it didn't expand past a certain point like it had a borderline; on the outermost part: I have little bumps other than that it's back to normal, middle going inward: u can see an reddish outline on the semi cured part and in the innermost part: skin is smooth no longer flaky-looking but still dark discoloration. They recommend taking vitamin D, I think the cold weather has something to do with it like skin not being moisturized. They also recommend taking shorter showers with lukewarm water. I still take long hot showers 🙈