I'm unsure

I have always been irregular with my period and the last time I had sex was maybe three days before it would have been a solid month since my last period. It's now a week and three days after my month and I still haven't gotten it. I have skipped months in the past and I did use protection. I heard there is a chance Precum can get you pregnant but his penis never touch my lady part until the condom was on and he didn't cum until like 5 minutes after he was already out of me. I'm stressed out and that might be the reason I haven't or I'm "late". But I never really know if I'm late because it's never the same. I've taken four pregnancy tests and they're all negative. Please help.