What causes irregular periods?

my period is late i was regular for few months now because of progesterone pills… now this month i havnt had any period. only light light when i wipe spotting and two times spot of dark blood on toliet paper diff days… never came… ive took multiple tests all neg except blye dye both were positive i tryed the spot of water test to see if it will fade it never did it got darker and clincal guard tests three of them had faint positives i did the water test they got darker… first response and dollar tree tests are all neg!!! and ive took alot of them!!! diff days diff morninggs and evenings… my last period was feb 13th for 7 days!!! have no idea why im late this month guess a trip to the dr soon to be put back on pills again… i have no sytms of being pregant my last two kids my first sytm was sore nipples and i have no sign of pregancy at all… it sucks because i was hoping to be pregant but at same time i wanted my period… :disappointed: