I developed a unusual rash, how long it would take to recover ?

Hi there, I m a 28 year old Caucasian female and back in June, I returned from Mexico, and within one day I developed this unusual rash that I ve never had before to the right side of my knee on my right leg that was red, itchy and inflamed; I never experienced any pus or blisters, it was just red thickened skin that was inflamed, itchy and very dry. I never treated, then it turned into a big inflamed patch that turned lighter than the skin around it (I ve tanned during the summer), so all you see is a big light patch that s around 5 inches in diameter. Then a month or so later I noticed a small pea sized white spot on the same leg and same quadrant of the leg (front and outside/right side of the leg). Then just recently I m finding that there are more lighter pigmented spots between that new pea-sized spot on and the original rash on my leg but all hypopigmented patches have really fuzzy undistinguished borders, and I ve also noticed a quarter sized inflammation an inch to the left of my right elbow (again, same side of the body, both right leg and right arm) along with other small circular dry (but not inflamed) patches just below my elbow, on the same direction, all also lighter in color than my tanned skin and slightly dry. I began treating it over a month ago where initially my GP suspected it to be fungal so I took lamisil that didn t do much. I was referred to go to a dermatologist, who then diagnosed me with Eczema and Pityriasis alba and prescribed me cortisone, which helped the inflammation on the knee, but because of fear of skin thinning I stopped using it 2 weeks ago, which a few days later caused the rash to return, I was really itchy and had many red bumps, but I ve been moisturizing it like crazy with Cetaphil and I can see dramatic improvement, however it s still slightly inflamed, and the hypopigmentation is still there and visible. After doing research on this condition it stresses that pityriasis alba occurs only in younger children or teens, so I m wondering if there was any possibility that I may have been misdiagnosed? Why am I getting it now? I realize that because I used cortisone, textbook definition eliminates it from being a fungal infection , is there any possibility that it could be bacterial or viral?? I just feel that it s spreading and can t contain it it s a little frustrating. What s the prognosis like? How long does this condition usually take for the skin to return to its original integrity ? Any suggestions would be appreciated. Thank you very much!