29 weeks Braxton Hicks 1st baby

Ancook3

Ive noticed my stomach tightening off and on for a while now but it never bothered me or came to my attention that anything could be wrong.  I went to labor and delivery last week because my low back was hurting me, they said i was having contractions but they were irregular and nothing to worry about.  The nurse said to come back in if I experienced all these different things and one was if the "contractions" were every 8 to 10 min or had more than 4 in a one hour period.  Ever since I came home from labor and delivery Ive been worried about my stomach feeling tight.  I notice it always seems tight like all the time.  Other times it will kinda tighten up(painless) and do it on and off a pretty good bit.  I timed it the other night and its hard to tell when its happening for sure but I noted 8 times within 1 hour.  Is this normal?  Could it be related to gas?  Or could this be early stages of preterm labor??  Im hoping some other mamas or mamas to be have experienced this and can help me out.  I dont wana be that paranoid woman going in and out of labor and delivery every week for no reason!