Not STD. Not heat rash, either, probably, as those are just irritating and then go away. Probably just chafing. Not a place likely to get eczema. You might need a better pair of bicycle shorts. I used to get friction rashes all the time in that area from running. If it was just itching and not red, it might be ringworm, or jock itch. That's a fungal infection, but those are more likely in the edges of your pubic area where it's nice and moist. But if it's been two weeks and hasn't improved at all, have you been exercising in a way that still causes it to rub in that area? Does it hurt when you rub against it? If it doesn't hurt at all when it gets rubbed against, then it's less likely to be a friction rash and more likely to be fungal, in which case if it goes on much longer you'd need to see a doctor to get a diagnosis. But if as I suspect it's from that bike ride, applying a good quality natural moisturizer several times a day will help. In all cases, though, we're only guessing, and the only way to ever know for certain is to get a diagnosis. Peace.