Spotting and cramping

I'm 20 weeks, today started having a bit of brown blood spotting.  I'm hurting but not severe, it's just very uncomfortable.  I started contracting at 27 weeks with history is I do have a shortened cervix and irritable uterus which makes me contract sooner and sooner with each pregnancy.  Ellie was 10 days early, Emma was 3 weeks early.  My pains right now and the spotting of course is concerning so I wondered if I should call Doctor. Trying to just lay down and drinking lots of water in case this is just dehydration.