Dark patch - scrotum, can we lose them?

I always had dark patches on left and right side of my scrotum, but bigger on left side, I thought it's due to sweat and I usually sleep on my left side. Recently I haven't been bathing regularly and since it's summer I've been sweating a lot too near groin area, the dark patches spread towards thighs and maybe under the scrotum too, and started itching really bad. This may be jock itch the skin color is little red I guess when I wash it but mostly dark in color and the texture of the skin is also different. I've two doubts can the tinea cruris become so severe suddenly? Because I didn't have any itch few days ago and suddenly it spread really fast. And after this I've been thinking the dark patches I had in the past, what are they? Were they really just due to sweat? I didn't have any itching sensation or anything like a disease before, but the texture of skin was bit different. And also, this looks bad, how long will it take to cure if I use over the counter clotrimazole? Thank you.