QUESTION!!!!!!!

So my boyfriend and I been having sex for about 4 years now. So we starting having unprotected sex about 3 and half years ago and not once have I gotten pregnant. We have had many many many i mean many slip ups. pregnancy is the last thing on my mind but my question is should i be worried about not being to be pregnant?? What should i do??? I was on birthcontrol in the beginning but after 5 months i got off... so its been at 3 1/2 year could that be a reason???