over-watering or poor drainage is an issue, imo. see how raised and puffy the leaves are? re-pot to a 6" pot or gallon container, and let it bounce back. no nutes til you say to yourself, "self.....that little fucker is really starting to grow." and then only 1/4 strength. when it perks up, put it outside in the shade for a few days, and slowly acclimate it to sunlight.