Yes, STITCHES is a Scrabble word!

Letter values in Scrabble US: S 1, T 1, I 1, T 1, C 3, H 4, E 1, S 1.

Is it a valid word?

STITCHES is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a link or loop or knot made by an implement in knitting, crocheting, embroidery, or sewing
a sharp spasm of pain in the side resulting from running

Also: run up, sew together.