I agree with possibly too much nutes... make sure you are using any flowering nutes and have moved to the bloom nutes... also make sure your soil is dry before watering. Possibly even a touch over watering IMO... do a couple feeds of just water before giving any more nutes. For most part nutes should only be fed 1-2x a week depending on your watering schedule. 3 weeks into flowering, your plants should be getting water probably every 2 days, with your lights (CFL) that I see probably even longer 3-4 days, but again pay attention to your soil.