I am 27 weeks prego and I'm having quick & sharp pains on the left side of my uterus. I have been constipated so could that be whats causing them?

Could be. Constipation is certainly one possibility. Try fixing that by using Miralax (polyethylene glycol) or milk of Magnesia. If that does not help you will need to see your Obgyn to determine what is going on.