Whats wrong with me?

My grandparents pointed out today that I have not been my self lately. I have stopped taking my anti-depression pills about 6 month ago. some days ill be having a great day and no one can ruin it, other days I feel down in the dumps and have not been the greats person to be around ( I don’t get mean or anything its just I have no energy to do anything). I have exams coming up next week, is it stress from that or a mood swing from not taking my drugs in so long?