Weight fluctuation can definitely cause your cycle to change. If you drop too much weight too fast (or you get underweight) it also will cause you to stop having a cycle completely.
Many things such as stress, diet change, malnutrition, medicines, illness, exercise, etc etc can all affect your period. If you don't mind my asking, what's your current weight now?
i was 139 and im now 127...i wanna weigh 120-125 because im 5 feet tall and curvy...