I Am Planning For Hyerstoscopy For Endometrial Polyp,I Got Ultrasound

I am planning for Hyerstoscopy for endometrial polyp,I got ultrasound done last year for same. Twice,Polyp was detected but recently when I got it done it was not detected. This time Ultrasoubd was done on the 3rd day of my period,what may be the reason for same..does polyp not exist now?Also one of my fallopian tube is open while another had Delayed spill in HSG test,pls suggest should I go for Diagonstic Laproscopy.