I am sure this has been posted 50 thousand times or maybe I am just too dumb to figure this out.

This is my first two color garment.
I am knitting a baby sweater with Baby Cashmerino in stockinette that has two row stripes. So, I knit one row, purl the next, switch colors. Certainly I don't have to cut the yarn and rejoin every two rows. How do I carry it up the side seam or something like that?
Thanks for your help!
K