Period was very light and stopped on and off the last time i had it. more like spotting and i'm not pregnant. what is wrong?

Can be many things: Many women will periodically have irregular menstrual cycles at some point in their lives and there is not necessarily anything "wrong" with them. Sometimes medications, stress, diet or weight changes, exercise, etc can affect your hormonal cycles and/or ovulation in a given month with resultant abnormal periods. If this continues to be a problem see your primary care doc or gynecologist.

Perhaps nothing: Most women have predictable periods so it seems something must be wrong if things change. However menses can normally vary. If they generally occur once a month then probably all is well even if the amount of flow varies . One should get concerned if skipping for several weeks happens, if the periods become exceptionally heavy, or if there is substantial bleeding between periods.