Please Help!!! Any Ideas?????

I’ve been in birth control for about 3 years now. I have my periods every six months (recommended by doc cause of bad cramps and irregular periods). Every time I want to have a period I simply stop taking them for a week, and around the third day is when I have them. However, I haven’t taken them for about 2 months trying to have a period and I STILL WONT HAVE ONE. I had sex unprotected a week prior to not taking them and have taken two tests 3-4 weeks after having sex and both are negative. Any ideas?! I never prayed for a period so much in my life.