Pregnant on PT but not pregnant on ultrasound

on my case this is very peculiar.. cause i have regular period tas biglang nagkaganito.. i had done 3 TVS and i had to accept that there really is no baby or gestational sac/embryo developed..but still my PT were still positive if mag take ako at anytime of the day..and the question na hindi pa nasasagot, why is my left abdomen at minsan nasasamang sumasakit left butt and leg ko..sa tvs wala ring nakitang ectopic or any complications..so what causes it?any idea moms?#4thPregnancynaSana