Also, don't be discouraged about seeing a doc and having to tell them that you're unmarried and 16. The obgyns i've encountered including their nurses/medical assistants are the nicest docs i've ever met in my life. I never go to the doc, but i'm always excited to go to my monthly appts.
You've missed a couple of scheduled tests already so I don't know how that'lll affect you (you've missed a blood draw at 18 weeks to measure your afp levels, a couple ultrasounds, and sometime during your 24-26 week you should be starting your glucose testing).
If you need financial help, the doc's office may put you on sliding scale to reduce how much you have to pay based on how much you make, there's also a maternal card of some sort that helps pay for costs, and welfare. If your parents have insurence, you may be covered under your parents plan. I work full-time but i'm under my mom's plan because it's way cheaper being in a family plan and they cover my obgyn costs until the baby is born. For me, i've already met my deductible for the year and any additional doc appt are covered 100%. So there's another plausible reason why you'd want to mention it to your parents.
Again, good luck.