Personally i've had the same problem. Time and time again my plants, never seem to match up to other grows and I give them a shit load of good nutrients. Honestly it could just be a bad seed, but after a while you wonder. In an attempt to increase my yield, I LSTed and pruned my plant and it's easy to see now it's waayyy overdone. Lesson learned is, not to over due anything with plants. Clearly u didn't do any of these things, but perhaps you are over doing something very minor like watering. Remember your only supposed to water when the soil is pretty dry and your leaves start to droop. If you water every other day, try watering every 3-5 days. I'm in northern cali and i notice my plants do just fine without water for 4 or 5 days. Good luck with your grow man, it might just be your first crop won't be enormous. I'll tell you i've killed at least 20 seedlings this year and it still hasn't stopped me from trying.