What Causes Irregular Periods While On Birth Control Pills?

Hello, So this last fall I had ran out of my birth control pills and did not immediately go to the doctor to get more. I did not have a period for months and so my doctor gave my a pill to jump start my period so I could get back on the pill. I did that and had multiple periods that interrupted my birth control pills. I decided to stop taking my birth control for good in January. Since then I have not gotten a period. So about 3 cycles. Is there a way to regulate my period? I ve always had irregular periods and I potentially want to start trying for a baby the end of this year or next year. I took a pregnancy test a couple weeks ago and it was negative. I bought one today that I m going to take to be positive but I don t think I m pregnant.