I think my plant is not growing.

At this time of a cannabis plants life, when it is transitioning between veg and the beginning of flowering, it is undergoing many hormonal changes which can cause an almost "stagnation" of progress while it moves from one phase of its life into the next. All this is normal and nothing to be concerned about. In a week or so it should power away flowering.

The main thing to remember is if the leaves are a uniform color that isnt a healthy green its micronutrients (sulfur etc) or general soil conditions (pH). If the leaves have green veins and pale leaf bodies, non-uniform color, the plant is lacking N P or K and the uneveness is from the plant redistributing where its scarce resources are used. Only thing I can think of that would effect the green across the entire plant is a disruption in chloryphyl. I noticed the serrations on your leaf look to turn upward which is a sign of early hear stress/intensity. Chloyphyl at a atomic level has a magnesium core. Epsom salt with no dye is just another name for magnesium sulfate. Throw some in a spray bottle and spray the underside of leaves. If it happens to be magnesium you will see color change to normal rapidly/overnight.