Can you get birthmarks later in life ? Help please. ?

I know it sounds stupid. & I know people get birthmarks at birth. But awhile ago I noticed this light brown patch on my inner thigh. It's the size of half of my hand. & I'm very very pale so it's noticeable. I also already have a large birthmark on the back of the same thigh. That one is much bigger than my hand & very dark. It's also not cancerous if that means anything. I'm just kinda worried about this new "birthmark" I'm scared that it'll get bigger & connect to my other birthmark ;P i don't want it bigger. & I also have vitiligo... My skin pigments are dying so if I get tan some spots of my skin will stay white since the color changing pigments are dead. So does thar have to do with anything ? Please help. Thanks.