First of all MG is the worst thing you can give to an mj plant Burns way to easy and if you dont flush before harvest your weed is going to taste like shit. Try to stay organic if you can fish emoltion, bat guano, fox farms big bloom, tiger bloom, ect. Depending how much mg you have given it it might no flower for a long time. If a plant has too much Nitrogen it wont flower. Your plant should have started flowering about a month ago