I planted a few seeds of a lemon from a friend's organic tree July of 2016. The tree has been growing great. It smells beautiful and is developing great little thorns. My issue is the a couple of the leaves are tightly curled under and some are yellowed. I have not yet used any fertilizer as I am not to familiar with what type I should use as well as if the tree is old enough, if that even makes a difference. It has spent most of its life in a good majority of sun, but most recently has been in an area with indirect sunlight throughout the day in fear of the possibility it was getting too much sun. Also not sure if that's a thing. I have it in a basic cactus/citrus soil mix and let it just about dry out inbetween watering. It seems like a pretty healthy tree, but I know it's trying to tell me something. Not sure what type of lemon tree it is specifically, but the lemon the seed came from was off a rather large fruit bearing tree and the fruit quite bitter and juicy. If anyone has any ideas what this little guy may need I would appreciate any tips and recommendations! Pictures below