Confused and scared

So I am on the shot and I got on it in September and my SO and I had unprotected sex for his birthday on October 18th and he came in me. However, I was supposed to start my period the 2nd and now I am 5 days late. I took two tests and they both came out negative so I'm not sure if it's my body still adjusting to the shot or if something is actually wrong. Any advice?