Could be the start of something, but then again unless you are one incredibly lucky person, things WILL escalate to something undeniable eventually. At which point you will know to call the doctor.
It could be some mild early contractions, the baby dropping more, more pressure on your bladder, etc. I'd suggest since things are close to rest as much as possible. If the cramping continues to get worse after a good nap, you'll know you are progressing towards delivery.
With my 2nd, I had my membranes stripped around noon. Started some mild cramping around 4 that day. Attended a halloween party at DD's daycare from 5-8 pm, as the cramping grew worse. Got home, put DD to bed, and by 10 pm the cramping had shifted to good old contractions. DS was born 6 hours later. What. A. Long. Night. I wish now I'd been smart enough to go straight home and take a long nap before spending the night in labor!