Cramps when I run?

Yesterday in gym class we run a mile. This is not the first time this happened to me, but after just about 2-3 mins. I got this cramp contained by the left side of my stomach. (P.s. it have nothing to do beside my period)
I asked my gym teacher, and she refered to it as "stiches?" she said I am breathing one and only threw my mouth and not useing my nose and specifically causeing this. She told me how to breath correctly when running but I forget what she said. Can someone tell me if she is right more or less what this is? And why do I get it? How can I prevent it?

Im trying to draw from into great physical shape so any info whould be great! (P.s. Im not fat but I still want to be without fault fit or at least as close as I can gain to it and I cant do that we this frickin cramp I get!)
Answers:

Any longterm Fioricet/Fiorinal users or abusers own advice for me & how it have affected them?

your gym professor was correct !
Breath thru your feeler and out your mouth.

Does Birth Control make or motive weight gain?

start doing situps and crunches every year before conservatory. Learn to breathe properly like the gym don said. In your nose and out your mouth. You will catch there...perfect luck!

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she's right - its a stitch... usually it happen when you run/walk fast after intake, but i guess it can happen any time. im not sure roughly speaking the whole breathing thing, but a hurried way to bring back rid of a stitch is to stretch up, then bend down and touch your toes 3 times and the backache will go! it hurts the first couple of times you stretch up, but it works - i've tried it!