Sometimes ur body may be tellin u to "slow down" a little, cuz pregnancy is different with exercise. You can walk, jog, swim, and do anything else thats safer, but ur not supposed to lift weights, ride a bike, etc so ur body may be tellin u to stop what ur doing and to find something else.
I wuldnt wory too much about the cramping unless there was blood, or clotting. So dont worry!
Shauna