Was this preterm labor and why?

My doctor took me off work last week and I just went back on Tuesday. Tuesday night I had severe menstrual like cramps, backache, nausea, diarrhea, and strong pelvic pain. I had painful contractions coming every 2 minutes at one point, lasting 5 hours. It stopped and didn't come back so I haven't asked the doctor about it yet.

What was this? I was expecting the same thing tonight but nothing is happening. I seem to have more BH contractions when I work too. But I have an office job where I sit most of the day. It couldn't be that could it?