Ultrasounds during pregnancy

How many ultrasounds do you normally have in a pregnancy? I'm almost 15 weeks and I already had 5 ultrasounds including NT at 12w.
First one was at 4w because my last period was off and my Gyn wanted to check for cysts. 2nd at 6w, 3rd at 8w with my OB which I didn't like and changed after that dreadful appointment. 4th at 10w and last one was the NT. 
I'm a little bit worried about overdoing this. With my first pregnancy in 2008, I only had 4 ultrasounds throughout the pregnancy.
I'm not high risk.