Are you not seeing an OB? If you are I would wait until they schedule one. They'll do so between 18wks and 20wks. If you go somewhere on your own you'll probably have to pay for it yourself but if the doctor's office does it insurance will pay.
the 3d ultrasound places will do a gender determination for about $50 to $70 depending on package. it will all be black n white with a peek in the 3D its a great keepsake and a great experience!
Google ultrasounds in your area.