My first guess is pinworms. They tend to become extra active during the new and full moons, and the itch is like no other. My second guess is perhaps you made the area raw from itching and opened the skin to getting now a yeast or fungal infection, as it would be the only cause of a rash that spreads, not the pinworms.
If it's pinworms, May God have mercy on you. They are nearly impossible to rid yourself of. You can take over the counter meds or prescription, but they don't seem to help. humaworm is another option