Rash for 1week between leg and groin area. slowly spreading only on one leg. itchu at night. no pain.

Rash: This sounds most like a fungal rash that needs a cream to treat it. But to be sure you must see a doctor in person. It can be other types of rashes.

Jock itch: This is the lay term for a common skin fungus usually acquired from contaminated fingers touching the area. The fungus can be found in the soil, on animals (ie.dogs) or other humans. Many over the counter creams,lotions or sprays can be used to self medicate. Clotrimazole is one of many. Use daily for a week or two will usually fix it if that is the issue. Your doc could confirm/exclude it.