Won’t regulate

I have been on birth control for over 5 months and my period still haven’t regulated, I have been to the doctors many time and they just said it takes time but i am still getting it every 2 weeks and is so unpredictable and I was supposed to get my period on the 25th but I didn’t and I have something big on Friday that I don’t want my period for and I feel like I’m going to get it the day before and be on my heaviest day on Friday😭😭😭