9 Day Late Negative Test

I'm feeling so lost and confused. I had sex just a couple of days before my period, around the 3rd/ 4th December.
My last period began on the 9th November so I'm now 9 days late. I've taken a clear blue pregnancy test this morning and it said not pregnant. Is it even possible to conceive so close to your period. I've never had a period later then 2 days so I'm now worried there's something wrong with me.