Filut I had the same prob my first couple of grows (V.Kush , Gdp , Big Bud , Trainwreck , H.Gold etc) a good yield and regular bud.. I thought it was everything from my nutes( brand , or too much/less) to my bulb being shit. So i went out & bought a 8ffy of some sour , and to my luck it had a seed in it.
Long story short i grew her out with little to no love( feed 2x , cfl lighting , etc) and she was the BEST BUD I EVER had , my freinds stiil talk bout her and hope shes coming back..
The moral of the story is I feel its all about GENETICS.. Good Luck!