I am 24 and i been gaining weight and my period wasnt nomal for this month. but i took a preagnent test many times and still negative. whats going on?

A few ideas: Extremes of weight (thin/heavy) can cause changes in menstrual cycle. Excess weight gain without changes in diet or exercise, can be due to increased stress (working night shift for instance, missing sleep), or thyroid or prolactin. You may want to see md for an evaluation and testing. If your bmi > 30, that could be playing a role as well.