Q: Stalling when stopping reverse

I own a 2 wheel drive pick up. It began to stall unexpectedly when I put my foot on the brakes. It didn't happen very often and the truck would always start back up instantly. But it doesn’t want to start at all now. When it does start it wants to stall right away while sitting at idle or when I put it in reverse. I went shopping this afternoon and it stalled on me again. I had a very difficult time trying to get it started this time, too. I had to drive with one foot on the gas and one foot to be ready for the brake to get where I was going. I didn't want to let my foot off the gas if possible. Do you know how I can keep my car from stalling? What should I do?