Is It Advisable To Wait For 3 Months To Do An Ultrasound?

Hi, I am 36 years old and just had a transvaginal ultrasound and found out I had a thick endometrial lining of 20mm. My family doctor said to redo the ultrasound in 3 months closer to the beginning of my cycle. I have had some spotting and cramping betweein periods and heavy periods with large clots. Do you think it is a good idea to wait 3 months to have this checked again?