What Causes Vaginal Spotting Despite Regular Intake Of Primolut?

Hello, i have been having long periods and i did an ultrasound and found out that i have fibroids. a doctor put me on primulot for about three months without periods. i have been taking them three times per day but i still spot, like if i do not take it in time i start bleeding again, why is that? this is how i take the primulot: in the morning at seven thirty, then after twelve in the afternoon and around eight or nine in the night. however, almost every morning i wake up i am bleeding alittle, then i take the pill and if i take long to take it by twelve lunch i am bleeding again and so it goes, one i am not certain hours to take it i start bleeding. please help me understand whats going on