My dog is really itchy lately, she has always been a little itchy but not this bad. She doesn't have any fleas or bug bits, I just checked her good and the only thing I found was a little loss skin in a spot the size of a pencil eraser and the skin under that is it's normal gray/blue color, I couldn't find anything else. I've tried oatmeal dog shampoo that I got at Wal-Mart, but it doesn't seem to have any effect that I can tell. What should I do, that won't cost me an arm and a leg?