Backache/cramping

So I'm 19 weeks 1day and I've begun cramping...it's been intermittent my entire pregnancy, but this is different. My back began to hurt and after a bit, I began cramping really bad, but then sat for a bit and the cramping went away...have I just been overdoing things? I work 30 hours, attend a university every day, have a 6 yr old, and live on my own with my husband...or should I be concerned?? No ob apt til next week!