Is consistent visible swelling only on one side of face normal 3 weeks after a Facelift?

The swelling at 3 weeks after a facelift and fat grafting should be gradually but progressively getting better at this point.  By 6 weeks after surgery you should be 90-95% of the way there, but it may take 3 months before the swelling is completely gone.  Generally, the swelling is the worst right in front of the upper part of the ear and down in the neck right below the ear lobe.  Asymmetry to your face is common both before and after surgery, but should never be dramatic or noticeable to the casual observer.   

Asymmetric swelling is not uncommon in any surgery.  It is important to note these asymmetries to your surgeon and help determine why there is a difference.  It may take 6 months to a year for your face to fully heal so be patient if necessary.

 It's impossible to say from your description but significant asymmetry of swelling should be reported to your surgeon. Nobody  heals symmetrically but your surgeon can reassure you that this is a variation of normal and not a collection of subcutaneous fluid that should be drained.