Completely irrational fear of pregnancy

A month ago, I lost my virginity to a guy I hardly even knew and lately I started noticing some very weird changes. My hormones are raging and out of control. I'm getting nauseated more easily with certain foods, I'm more emotional and I've been dealing worth mood swings. I'm even late for a period by almost 2 weeks. I'm on birth control and a condom was used, but I'm still scared I could have gotten pregnant that night. I took a test last week, it came back negative but I was drinking a lot of water and I was told it can show a false negative under certain circumstances. I don't know what I should do..