DO NOT DO THIS!
This is not an uncommon sight to see. STOP right now! It does not matter how heavy your purse, laptop bag, or luggage is, the fact that it is on your shoulder will skew your body alignment immensely!
What do you think would happen to this person if this was what they did for 2-4 hours per day, for the next, say 5-10 years? Enough said!
Solution:
A messenger style bag with a long strap that crosses the chest. Once in while you should alternate it from one shoulder to the other.
That should straighten you out!