Our Week Starts on a Sunday????

What? This is just getting to me. Why in the world on our calendars does it begin with Sunday. First of all, there are week days which include Mon-Fri. Then there are week ends which include Sat-Sun. Should not our week end on a week end and begin on a week day? I mean, it is stated in the Christian Bible that God created the earth in 6 days and rested on the 7th. Is not our rest day Sunday? That should be the last day of the week, not the first!!!!!! When did this go wrong. It would be too late to change it because it would mess every thing up! It will be this way forever unfortunately