What Causes Sudden Shortness Of Breath In Runners?

I am a middle distance runner (10km-14km) total of around 40-50km per week, I also do some strenght 3 -4 times a week. Yesterday (2feb) I felt like I had gas, I couldn t run a km without getting a stitch and I was out of breath so quickly even at my jogging pace! Do I have an allergy? I have never felt this before.