contracting since 2nd trimester

Has anyone else been contracting since 16wks or earlier? I'm now 33 weeks and have contracted since about 16/17 weeks or so, at first my doc was concerned, but after 3 negative FFT (test for protein to r/o premature labor) and my cervix being 2.7cm long thick and closed, my doc figured I just have an irritable uterus and will watch me closer considering I've had preterm labor with my last pregnancy at 27 weeks with my first child. Does anyone else have an  irritable uterus??