FTM Contractions

I have no clue what I should be looking for with contractions. I got my membranes stripped this am, dilated to a 3, 80% effaced. She told me to go home and walk, which I did two miles and then do nipple stimulation to get the contractions going.  All I've got is back cramps occasionally accompanied by my stomach tightening. It's uncomfortable but manageable. Any advice on what I should be looking for?