It is difficult to recommend treatment for a rash without knowing exactly what the cause is. And to diagnose the nature and cause of a rash, one would need to see it, or at least have a detailed description of it. Your description is too brief - rashes are typically red, but apart from this there may or may not be swelling, blisters, bumps, spots, flaking skin, or sores. You may also experience pain, itching, burning, or no unusual sensation at all. The list of possible rashes is too long to even begin.
Trying to treat a rash without knowing what it is and how it was caused may end up worsening or spreading the rash. However, there are a few safe home remedies that you can try before you visit your doctor. Aloe vera gel is safe and soothing, and at the very least eases most skin conditions if it does not cure them. Vitamin E is also good for the skin and is available at most medical stores as an oil. You can also take a Vitamin C tablet once a day, and apply a crushed tablet or two mixed with water to the rash itself. If the rash continues to spread or if you see no improvement, you should show it to your doctor.
answered by G M