Hi, I can understand your concern for on the thighs, lower back and pelvic area. There can be multiple possibilities of the lump 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 either an allergic dermatitis rash or a simple bacterial infection or it may be fungal infection too. 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. All the best