Warming up and stretching are not synonymous. Before running, muscles tend to be cold and tight, and a lengthy prerun stretch session may tear a muscle. Instead, start your run with five minutes of jogging to get the blood moving, and save the stretch session for after your run to increase flexibility of your warm and tired muscles.
You should also try a dynamic warmup to prime the joints and get the muscles ready to run. High-knee marches are a simple way to get heart rate up, but here are more moves to incorporate into your active warmup.