I'm not even going to try and guess what's wrong with this plant because I don't have anywhere near enough info about your grow. It could be over/under watered, over/under fed, could be nutrient lockout from high/low soil pH, the list goes on. For future reference, when asking for assistance with a plant you should include the following info in the post....
Type of soil/medium you're growing in
Type of light/s you are using and total watts of said lighting
Maximum/minimum temperature and humidity in the grow space
How often, how much, and what you are feeding the plant
Plus any info on if and when you've transplanted, trained or otherwise messed with the plant/s....
Knowing these things will help others help you, and keeping good records of these factors will make you a better grower and less likely to have to ask questions in the first place. Good luck.