My right arm is very blotchy??!!?!

On my right arm there is a bunch of red blotches, they have been there since forever. They don't hurt or itch at all. I briefly asked a dermatologist, but she said, without looking very closely, that it was a birthmark. But it goes all the way up my arm, but my other one has it very slightly. It gets almost purple when its cold, and there a few of these little pure red dots, not bumps, just like someone marked me with a red pen. I included pictures so if you can identify it, send me to someone who could identify it, or tell me how (if possible) to treat it.