How long does oral birth control stay in your system after you stop taking it?

I am 26 and I stopped taking my oral birth control in February after being on it for 4 years. My periods have always been regular. I was on it because I had hormonal acne and painful cramps. After stopping it, my periods came right as scheduled and flow was normal for me. I'm asking because my husband and I are trying to get pregnant and have so far been unsuccessful. I have looked up how long it stays in your system but have gotten conflicting answers. So ladies please lend me your knowledge and personal experiences! Thank you!