Please help

Ashley
My period usually comes a day earlier than what this app predicts, but this month it didn't. It was predicted to come yesterday, but didn't, and so I was expecting it to come today, but it hasn't.
And while there is no blood, I have been having some weird brown discharge that I've never had before, and when I looked that up, Google points almost all signs to being pregnant.
I'm 18 and do rarely have unprotected sex, but I'm usually on my period when doing so and were very very good about pulling out. Usually I get stressed out during and have him put a condom on anyway.
I took a pregnancy test and it came back negative but I'm still very worried and I know that being stressed will only make all matters worse.
If anyone has any similar experiences or any advice at all id be so appreciative! I definitely DO NOT want to be pregnant right now 😕