What Causes Blotchy Rashes On Legs, Elbow And Stomach?

I have a blotchy rash on parts of my skin (legs, elbow, stomach, neck, etc) and it forms in a linear pattern on my stomach and buttocks. I thought it was poison ivy and applied treatment. I recieved some relief from the itching but it has been two weeks and the symptoms persist. I have searched online for other possibilities, but to no avail. Any suggestions as to what it may be?