I'd think early labor first, appendicitis second. If you haven't yet, call your doctor's night line for advice, or go to the ER.
Could be a number things. Try drinking a bottle or two water, could be your fluids are low and it's causing cramps. It could be gas and/or constipation, in which case the only thing for relief is to work the gas out by moving or having a bm. It could be false or early labor. If you've seriously been in pain for 8 hours and it's so severe you can't move than its probably time to go to the ER and get checked out.