Late period possible pregnancy help

So according to the app, which usually predicts my period within a day or two, I was a week late. For someone who has had her period since 5th grade and never late, that's a weird thing. I did have unprotected sex on the 11th. I guess my question is, for those who had implantation bleeding, was it different than your period. Also, for those who had an actual period that first month, was it different than your others? Mine have been heavy since I had my baby and as of right now this is a lighter. Not much on a pad but I do have blood when I wipe. Sorry if that's too graphic. Just trying to figure out what to do next.