Too many ultrasounds?

I'm currently 10 weeks pregnant and have had two vaginal ultrasounds one at 6 (because of pain) one at 8 weeks (follow up) and one I'm going to get one at 12 weeks then another for gender around 18-20 weeks.. Is this too many? Can they be harmful? I've heard it doesn't really make a difference then I heard it does... Any thoughts? How many have you had?