+1 on the breathing. I read somewhere to take a deep breath and exhale FULLY two or three times, then gradually increase your breathing back to normal. It seems to really help. Thinking about relaxing your body when you do it helps.

I did have a period where I got side stitches and just could NOT get rid of them. I went and got a massage and he dug around in my diaphragm and ab muscles and loosened them back up. Maybe some core stretching would also help.