My red marks have faded a lot and my skin actuallylooks completely fine. But as soon as i run warm, they appear like red christmas lights. Why is that? They become like fresh marks even thought they're about 6 years old. This bounds me to wear make up even though i look completely fine in the morning, because i know they will become "visible" later on in the day. Is this even normal?
I have the same problem as you do! I've seen a post about it on here before, and I can't find an exact reason. Some people believe that when you sleep, you get less blood flow so they're less visible. As for taking showers and such where you get hot, that will certainly make the red marks appear more defined.
You're not the only person dealing with this! Just wish they could go away. 
Often the treatment for this is laser vbeam or quadrostar pro, its a vascular laser for veins and arteries. What your describing is when your flushed, warmer or cooler, or more active, some people even get Rocesea and flushing.
You can also read this here.