Last period on 13 dec 2013, I had sex on 14th jan. Ejaculated inside me. No period till 24 jan. Regular periods. Negative pregnant test. Chances of pregnancy?

Unlikely. If you have a regular 28 day cycle and the first day of your last period was december 13, your "fertile window" was somewhere between dec 22-dec 30 so pregnancy unlikely if that scenario applies. You are now 9 days late for ?Unexplained reason. If concerned, can either wait or get a pregnancy which should be positive by now if pregnant.