If your inseam is 29.5 an XS may not be all that far off...perhaps a little bit too small, but I have a similar inseam and my mtn. bike is an XS...I got a good deal on it brand new. I'd probably fit just as well on a S (I've ridden a S Salsa Mukluk, but a friend who has nearly identical measurements to mine rides an XS).

Does your saddle have a cut-out? If your sit bones don't hurt (I assume you're a fairly new rider?) I wonder if you're putting enough pressure on them. I get badly chafed from a lot of cut-outs, but without a cut-out I suffer seriously bad pressure up-front. My pelvis seems to be rotated forward with spinal lordosis, so I have a dickens of a time resting my weight fully on my sit bones. Could this be a potential issue for you, too?

Maybe your reach is too far for some reason, though that would surprise me, given your height and bike size, unless the stem is really overly long.