Beginning of labor?!? Advice!

Hi all, I will be 37 weeks on Tuesday. This past Wednesday at my 36 week check up I was 1-2cm and 60-70% effaced and was nothing at my 34 week appt. I was losing my mucus plug in pieces last week and Friday I lost a big piece that was blood streaked and haven’t had anymore since. Today I have been having a lot of tightening in my whole belly and pains down low mostly on the left side and in my back that last about 30-40 seconds. I’m a FTM and don’t know if I should call my dr or just wait and see if it gets worse.. I hate bugging Drs on call if it’s nothing!