I had the exact same problem, but I would turn red anytime I was caught off guard - especially if it was around a group of people and I didn't expect to have to speak. I completely understand how you feel, and just like you, I wanted to quit my job as well. I can tell you this... it will never get any better until you put yourself out there. Unfortunately there are no easy fixes. The hard truth is you have to practice... nothing will help you like practice. I highly recommend programs like Toastmasters, Dale Carnegie or other local public speaking groups. You can also look online for audience simulators which would help build confidence if you practiced using an online audience. The main thing you need to understand is that once you put yourself out there, uncomfortable as it may be the first dozen times, you'll eventually stop blushing and actually look forward to presenting. Trust me, I'm living proof.
Hope this helps.