birth control/pregnancy

I was put on nexplanon on September  3rd. I had sex the 5th, we used a condom but for a while in the beginning it was unprotected. My period is 3 days late and my breasts seem like they are getting bigger. I honestly don't know if this just the nexplanon symptoms and I'm overreacting or if this is something more. if someone could help me that'd be great. thanks in advance