My period was one day short, is that sign of a pregnancy?

Hi I had my periods on the 1st of July till the 13th of july had sex on the 13th if july am I pregnant? ? But got my periods again on th 27th of july for 4 days bt I normally make 5....now on the 15 sep got my periods again bt for only 4 days and now am having period cramps is it normal or am I preg please HELP