The first date of my last period was december 31st and ended january 5th my next period is expected on january 26 th and i had unprotected sex this month on january 18th.. my question is whats the likelihood of getting preg week b4 my period?

Possible: If you have regular periods 28 days or so in length & the last one began on Dec 31, then you probably ovulated around January 14 or so. Eggs can be viable for sperm to fertilize for up to about 72 hours after ovulation, so intercourse on Jan 18 could result in a conception/pregnancy yes. If your next period is late, definitely get a pregnancy test done.