My Skin Tone?

I have a swaying skin tone. i was born very dark skin then around the age of 2 to about 6 I became super light. People thought i was iron deficient and anemic. I became dark again because of school. Around 7th grade I became super light again. Now i am just medium dark. How can I keep my skin color? I am 16 years old and is it normal for African Americans to have these weird light skin dark skin episodes. Will my skin ever settle? This sort of thing happens to my older sister also. Our skin changes are not tiny. They are dramatic but i don't seem to notice how much my skin changes from period to period until i look at a picture.
My Skin Tone?
It probably has to do with how much time you spend in the sun your skin gets dark to protect you from harmful rays in the winter you may lighten up because your body realizes it doesnt need the extra protection

leather handbag