Got any pics? Maybe the plant is simply stretching because the light isn't close enough. Drastic temperature and humidity an also cause the plant to grow slowly. Put the lights as close as you can without burning the plant. For flouros, this is usually a couple inches. Keep the temps in the mid 70's and not too far into the 80's with lights on. Lights off, keep it in the 60's. Humidity during veg should be between 40 and 60. I use a humidifier beside my intake to raise humidity to the upper 40's or low 50's. Without it, the humidity is right at 30 and the plants suffer. They grow, but not nearly as well. If your temps are too high (above 85) and you don't have CO2 supplimentation, the stoma close and transpiration stops. FWIW, that's a tomato stoma in my avatar. It's open and nice and happy...
Keep your grow environment like a pleasant spring day and you'll grow some fine smoke. Guaranteed.