Does your town or any bigger cities around you have like an "Ultrasona"? They do ultrasounds anytime you want but you have to pay out of pocket, Ohio has one in Columbus so I don't know if they're popular everywhere.

Thankfully my doctor did one at my first appointment(12 weeks) and my 20 week appointment, and I should get another one closer to the end, to see how big he's gonna be. I just find that odd that they only do the one ultrasound.