Wishful thinking?

My BF and I are TTC and as far as I figured it I was suppossed to ovulate around the 9th of this month. We had about 4 or 5 times during the "fertile" period, the last being this afternoon. While at work tonight I started getting cramping and I don't usuallly get any. What are the chances that this is implantation, or is it something else? I know it is WAY too early to take a HPT (I'm not due for AF for another 12 days) but I am just curious. Any ideas? How soon after implantation/fertilization do symptoms usually appear?