Is 3 weeks when I will see any results from ptosis surgery?

The swelling should not affect the final outcome.  However in the short term it may actually make the lid look lower since the weight of the swelling can pull the lid down.  If it was even post-op it would be unusual for it to fall at 3 weeks, but it can.  If still swollen give it more time to heal.  

By 3 weeks you certainly should see an improvement on the repaired side of the ptotic eye.  Some mild edema may be present but the eyelid margin should be higher at this point. If not you should inquire from your surgeon, if the repair has held in place