Inhn

For as long as I can remember I've had an annoying discolouration on my arms and legs. It's hard to explain so i'll try my best. The visible part of my arms are covered in weird little kind of redish-purpleish dots. Sometimes they're totally unnoticable, and sometimes it's so bad it looks like I'm dead. The annoying thing is that the other side of my arms which nobody sees is perfectly normal coloured, and I don't understand why that side is fine, yet the other side is so horrible looking. It gets me down so much I will only wear long sleeved things incase people think somethings wrong with me. It makes me upset when i have to do PE at my school because we have to wear shorts and short sleeved shirts, and some people have said 'why are your arms like that?' and I don't have any answer. Then there's other people in the group that have perfect skin and it makes me frustrated.
I have the same problem with my legs. Sometimes they look ok, but then out of nowhere they will go a horrible red-purple colour like someones drained the life out of them. It mainly happens when I stand up, but it's happened in many other cases. So I haven't worn anything but trousers in a while, I can't imagine happily wearing a skirt without feeling selfconcious.
My family is totally unsupportive, and when i get upset about it they think i'm being silly but it is so upsetting feeling so bad about my body, and I'm so confused to what the problem is because I don't have this problem anywhere else but my arms and legs. I'd appretiate any advice anyone can give or if anyone knows what it could be.
Thankyou