I did IUI 7days ago & have been reading that many women experience implantation bleeding & cramps. I only have sore breasts. Do most women experience it?

Implantation. Implantation of the fertilized egg occurs about seven days after ovulation or IUI . Not every implantation causes bleeding, but mild cramping may occur and you may have just ignored it. Your breasts are probably not sore yet because of pregnancy, but just due to the hormones made in the after ovulation phase of your cycle.
Variable. When doing IUI it's easy to start microassessing your symptoms, but they truly are variable. Take it day by day, try not to worry and fret too much, and pray for the best. Good luck. Remember, it's not if, but when.