Hi, I can understand your concern for itchy skin rash that started on thighs and is spreading now. There can be multiple possibilities of the dark brownish pigmented spots and it requires a close physical examination to diagnose the exact entity of the problem. In my view correlating with the facts you have provided it appears to be fungal infection of the area. I suggest you to meet a dermatologist to for proper therapy. In between you should wash the area properly. If I were your dermatologist then presumptively would have preferred to apply an antifungal cream such as clotrimazole or miconazole. You can take an antihistamine such as loratadine for once a day if itching is present. Do not try to pinch, pop or squeeze the area as it may cause secondary infection of the area. All the best