I have a rash on inner arms, part of torso, top and inner thighs and real bad on below the knees. Ankles and feet are a little swollen. No pain, but does itch. I woke with it Sunday morning July 1. Very hot where I am. Have used hydrocortisone 1 % cream and diphenhydramine HCI 25 mg tablets antihistamine for a little over 1 day and not much different except helps the itching. Cool shower feels good on it too.

This should be under Health > Medical.
But we can't diagnose a rash. It could be heat rash and you are doing the right thing. Some rashes are cellulitis, a bacterial infection, and need antibiotics. They start from a break in the skin from a cut or bug bite. Since yours is in more than one place, it sounds like heat rash or allergic reaction. If it spreads quickly, of course go to a doctor or clinic.

If it isn't better by when, should I go to see a doctor? A week?

I'd make an appointment on Friday for next week, and cancel it if the rash goes down.
Avoid scented soaps, rinse well, pat dry, walk around/lie on bed naked until totally dry. Wear loose natural fiber clothing, no tight jeans!
You can buy spray cortisone too.
If it spreads rapidly, go to an ER.

What about the swelling in lower legs, ankles, and feet? Is it a concern? Is that enough to go see a doctor now?