I have no idea what's going on??

I stopped taking my birth control in march due to my sister having complications getting pregnant and we thought that might be why, so naturally I didn't want to have that be the reason I couldn't have kids in the future, but since then my periods have been pretty normal, just a few days longer and a little heavier. I haven't had my period for last month yet, as of right now it'd be 18 days late. I took pregnancy tests and they said I wasn't. Just a little concerned and confused. I've never been this late before.