So yesterday at my NST scan I was having mild contractions but didn't feel them, not even belly…

So yesterday at my NST scan I was having mild contractions but didn't feel them, not even belly tightening.Just now in the last hour or two my belly has been tightening on and off with cramping every so often. I know it's still kinda early, but when should I try to time the contractions? Or are they even contractions? lol I'm so lost