Why I am not able to conceive?

I ve been trying to conceive since last feb. It has not happened to me till this day. I have had a follicular study done and on Nov 30th I had a HSG done with everything in me completely normal... My last period was on nov 23rd and this month it was almost 10 days late.. I got it on Jan 1st... Why is it like this... I am always regular on my periods and this has happened to me twice i mean getting delayed periods one was two months back when i thought i was pregnant and the same this month too.... what is stopping me from getting pregnant....