Positive test and then a negative one?? Am I pregnant?

Last week I spotted for a couple days. Thought it was normal because I was in an antibiotic. I am on birth control. I got so sick and nauseous this morning and had a major headache. I got a test and took it around 4pm. It looked negative so I just left it on the counter. I went back an hour later and it said positive. I couldn’t believe it so I took another one right away and it came back negative. My period isn’t due for another 10 days. What do you think ladies?? Has this ever happened to you and you were still pregnant? Thanks for you help!