As Sandan209 mentioned, red face and other "stagefright symptoms" are very similar to a panic attack, where when you try to suppress them they just get worse. This is because those symptoms originate from fear, and when you notice them and try to stop them, that additional fear just causes them to amplify.
As someone who avoided going to college for several years because of my severe public speaking fears, I can definitely relate. Multiple factors eventually helped me overcome this, including:
1) Learning to accept/embrace the stagefright symptoms like blushing and shaking when they arose, rather than trying to suppress them
2) Improving my self-esteem (self acceptance) to a level where other people's potential judgment of me didn't matter so much
3) Realizing that if someone was judging/criticizing me, it was really they that had a problem worth judgment, not me.
Having been through this, I now have tremendous respect when I see someone experiencing fear/anxiety symptoms while speaking,but "doing it anyway". Try to remember that there just might be a few people like that in your audience, silently cheering you on. But again, total acceptable of your self and symptoms will likely do the most for getting you beyond the currently debilitating effects of blushing.
Author of MC2Method.com and SelfTherapy.org