light stress does that sometimes. make sure that your room is 100% light proof and they get a full uninterrupted 12hr dark cycle.
if youre golden on the light issues then its a grab bag of things.
giving more detailed info on your op through the plants life will yield more informative and concise responses from everyone. (soil or hydro, fem seeds, nutes, PH, temp, airflow ect ect)
good luck dude!`