I've Been Told That It Generally Takes About 4 Wks

I've been told that it generally takes about 4 wks for Celexa or Cymbalta to kick in, yet I seem to feel the effects as quickly as 2 days. my MD says that's not possible but I don't think my mind/body is making this up or It's the sugar pill effect (can't think of the name)... your thoughts?