What Causes Small Light Patches At The Back?

i beleive i have tinea versicolor. towards the middle nof my back is very light compared to the sides of my back. my chest from my breasts up is about two shades lighter compared to the rest of my body and the sides of my back has small light round patches. ive been using clotrimazole and i have been using versel selenium sulfide lotion 2.5 percent. is there anything that can clear this stuff up and by the way i have had this discoloration for about 4 years but didnt think anything of it till my sister saw it and i just started using these products last month