You should be fine and so should your baby. The whole reason for the sonograms are to track your progress to make sure your baby is safe. It is a darn if you do and darn if you dont type of situation but there has been no real proof that this is dangerous. Doctors tend to be over protective of the babys anyway and if they felt that harm would come to your child then it would not be considered unless medically necesarry.
I am now 35.3 weeks pregnant and I have had quite a few ultrasounds... I had oneat 4 weeks 6weeks and about 6 more so I would not worry about it. If you have any major concerns then I would ask your doctor....
Found this:
Safety Issues
Most practitioners consider ultrasounds perfectly safe, and strongly dismiss the concerns of anyone who questions this. However, there is a small but vocal minority of critics that contend that ultrasound safety is unproven and should be approached with more caution.
These critics oppose routine ultrasound with no clear indications for use, and generally believe that ultrasounds should only be used when their potential benefits clearly outweigh any potential risks. Other critics are not opposed to one routine ultrasound during pregnancy but are leery of the vastly increased number of ultrasounds being done today, especially with today's more powerful machines.
The point is that there are still safety concerns over ultrasound use, particularly with the newer technology. While there is no "smoking gun" set of studies that prove beyond a reasonable doubt that ultrasound is unsafe, there are still many questions that remain to be answered. Some caution seems to be prudent.
site: http://www.plus-size-pregnancy.org/Prenatal%20Testing/prenataltest-ultrasoundsafety.htm