Stomach tightening...is it a contraction?

FTM - I'm just over 39 weeks and for the past hour or so my stomach has felt tight and it doesn't seem to really let up at all. Is this a Braxton hicks contraction? I'm not in much pain, just uncomfortable and it doesn't really change when I change position or go from sitting/laying down to standing or vise versa. I see my doctor again tomorrow morning but is this something I should worry about now?