What are the chances i could be pregnant>>?

I had unprotected with my boyfriend a couple of weeks ago and i got the rod fitted 3 days later, i was told conception doesn't happen until 5 to7 days after so i was thinking that the implant would stop fertilization. It was only 2 weeks ago but my period was the week before so i can't take a test, i think i'm over reacting, i have many times before. But could i still be pregnant? And how high are the chances? thanks x