Yea, it could be that, but I doubt it. What you can do to find out for sure is wait and take the test first thing in the morning (the first time you pee)..the levels would be at their highest then. If it's still negative, then just know that havng sex can seriously throw off your cylce.
Same thing happened to me. My period was late but the test were negative. I used to have a cycle every 28 days (exactly) and it didn't come....but it finally did. After that, my period would come anywhere from like 32-38 days or so..... my cycle went crazy.
