What is this weird pigmentation on my leg?

i'm 14 years old & i have fair skin. recently, i tried jergens natural glow self tanner, and a few days later i found a light brown pigmented blotch on my ankle. then it went away. when i tried to use the self tanner again, a couple days later i noticed some light brown blotchy stuff on my leg. being a huge hypochondriac, i asked my mom if she thought it was cancer or anything and she said no. then today, i found this weird thing on my calf that looks kinda like a bruise but i know its not because its darker..