Hi, i have had a red mark the same size on my upper left leg close to the hip level. why isn't this going away and what could it be?

Doctor can evaluate: Question is vague. "Red mark the same size" has no particular meaning. Uncommon skin rashes, unusual spots, or interesting marks are hard to describe in words. One's primary care doctor or dermatologist (skin doctor) can look at it, maybe under a magnifying glass, and decide on a diagnosis. An in-person exam is best, but sometimes a video consultation with a good camera is adequate.