What Causes Delay In Periods ?

I got my period January 17th my period usually last a week & is usually heavy toward the beginning, I had sex January 24th & used a condom then I got A stomach virus that was going around the 26th/27th when I finally started feeling better I started slightly bleeding on the 31st for a few days it is now February 26th & I haven t got my period yet (usually around the 17th) am I pregnant? Or from where I had the stomach virus throw off my system?