I usually have 34-36 day cycles. however i am on cycle day 43. negative pregnancy test. i have always had a monthly period. advice? when should i see

Many factors: There are many factors that can influence/disrupt your normal cycle. These include (but are not limited to) stress, thyroid, medications, pregnancy, age. Something as "simple" as a move or a life change may affect your cycle. It's good that you are self aware ; however, do not worry too much. If irregularity continues, see your provider to discuss possible labs.