It's pretty normal for certain rashes to last three weeks or longer- you have mentioned that you get rashes regularly over the past few years- is this rash anything like the ones you are seeing? It could be something like eczema or psoriasis, you will only know for sure if you can get an exam- however, based off of what you are describing, I would lean towards it being one of those two. Psoriasis usually needs some ointments or creams to assist in healing- you can use petroleum jelly and moisturize the area. For eczema, you can likewise moisturize, but make sure you stay away from fragrance in laundry detergents, lotions, and other products you use on your skin. Keep track of your diet to see if there are certain things you are eating that set it off.
If neither of these routes help, you may consider contacting your general practitioner for an exam- a majority of the time they will work with you to get you in and help you be able to afford the trip. Feel better soon!