unsure

I stopped taking my bc pill on October 17th I then had a period during med November, which I assume was my withdrawal bleeding. I have not gotten a period since then and have taken a couple pregnancy test since mid November to now and always have gotten a BFN. I know that it can take awhile to get my regular period back, but my question is how often should I do a pregnancy test? I don't want to keep spending money on tests that keep coming up negative due to my period just not being regular yet, but I also want to find out if I am pregnant as soon as I can. So should I test every month, every two weeks? I'm just not sure 😕