Does the plant perk up when you water? If so, you're not giving them enough.... have you checked the PH of your runoff? You could have an imbalance there with a resulting lockout.... make sure the PH is between 6.0 and 6.5 with the "sweet spot" being 6.3 for uptake of all needed nutes and micronutes... The ONLY other thing I can think of is they're getting too much nitrogen which they don't need a whole lot of during flower and will often cause the leaves to droop...
Good luck!