Weird rash on thighs related to masturbation.

Hi,

I've been masturbating since I was 13, but never really did it the conventional way, I would lie down on my penis and just apply a little pressure. As a result I would usually ejaculate in my underwear and it would wet my thigh.
I've been doing it this way for almost 7 years now, but, when I was 15 I did notice a rash had started developing but didn't think much of it. It went away but it did leave my skin pigmentation on my inner thighs darker than the rest of both legs.
As of late the rash has come back and it's triggered off if
a) the room gets warm
b) I start to sweat there
c) If I so much as scrape my thigh with my fingernail.

It's really hindering my sleep because I inadvertently waking up scratching my thighs and it gets all raw.

I don't think it can be Herpes because I'm still a virgin, unless there's some part of Herpes which is non-sexually transmitted.
Also, the inner thighs, when they're fine is really very dry and almost scaly. If I stretch the skin on the thighs for example, it looks like the thinner grooves on people's palms.
Also, when it is all scratched the skin becomes quite bumpy.
The last bit of information which I'm certain would play a part is the amount that I masturbate. It can go upto 14-15 times a day and as little as 1 time in 2 days. It really depends on how much I'm at home.

I've been trying to cut back on masturbation but it doesn't really seem to help.

please help me!
Thanks in advance.