Hi!
In all probability this is sweat dermatitis. Keep the area dry, wear loose fitting clothes, and change undergarments at least twice a day. You can apply medicated talcum powder too.
It could also be a fungal infection like tinea cruris. Many treatment options are there like Clotrimazole 1%, Miconazole nitrate 2%, Tolnaftate 1%, ketoconazole, terfibnafine and Butenafine hydrochloride 1%. Many OTC products containing these salts are available, your pharmacist can help. Try a combination of two and apply until the round marks you see disappear. Continue application for 2 weeks after the marks disappear.
However, since a confirmed diagnosis is not possible on net, please show this to your doctor.
Take care!
Cheers! appreciated. Bit of stress taken away from worrying about it.