Couldn't be pregnant... Right?

So, I have horrible anxiety. My way of management is to keep my body free of any accelerates. I don't do sugar, soda, extra hormones or any medications. Including birth control. Any who, my husband and I use condoms ALWAYS. Well the last day of my period the condom slipped off afterwards and left a mess. I was supposed to have got my period today and it has yet to happen, I took a test which came back negative but am still worried...