It would help to have more information, strain, grow conditions, light schedule, where you live, PICTURES, etc...how does the plant look? My guess is that like DVD stated, it might be done with the veg cycle and its starting to flower but still you should experience some strech.. Is there anything else that looks wrong with it? It could be shocked, when a plant is stressed growth could cease, is it a Seed or clone? Did you start it outside? If not when did you put it outside? All of these factors could attribute to your problem. Then again nothing could be wrong at all.
SIFunk