Hi there Sega. Dont worry about your description. As a lay-person, it is perfectly understandable. The area that you describe in medical terms may be referred to as the perineum . To put your mind at rest, i personally dont suspect an STD. It could be & most probably is a frictional related problem caused by the thighs rubbing against each other if perchance you are carrying a little extra weight or it may arise on account of tight undergarments & /or sweating. Please do apply a cream containing betamethasone & miconazole (candid-B) is a common brand name but any such product would suffice that will also help get rid of any concomittant fungal infection. Do wash all your underwear in hot water & dry well in the sunlight to prevent any infections & weight loss may be in order. Good Luck & Godspeed! Dr Praveen Rodrigues MD