It sounds like you do get pregnant. Miscarriages are very common in the first three months. Estimates are 1 and 5 known pregnancies miscarry, the stat is even more often if you include unknown pregnancies. Still born is likely a totally different situation than your miscarriage. You would know better the circumstances of each situation of course.
If you have been having unprotected sex and have not become pregnant again, then I would worry you are having trouble becoming pregnant, but if you have been using some form of birth control, even rhythm or withdrawal, I don’t think you need to worry about being able to become pregnant.
You could consult a physician for some fertility tests. Reproductive endocrinologists check all the hormones and they are the fertility experts, but it doesn’t necessarily sound to me like you are at the point to consult with one. Your GYN can do some basic tests, but I would think if anything was obvious it would have been seen on ultrasound already from past pregnancies.
Also, if you get tests now, things might change by the time you get through with college, so you might want to wait until you are ready to try getting pregnant again.
Some basic tests to do would be make sure your thyroid is normal next time you are at the doctor, simple blood test, and if you become pregnant in the meantime by accident they should check your progesterone, not just HCG, thyroid, and take a baby aspirin every day. You could also consider finding a GYN who works with high risk pregnancies.