You can hear a babies heartbeat with a Doppler around 10 weeks. I would strongly recommend you go to a dr and get everything check out. It is really really important to get care early on in pregnancy, for your safety and your babies.
Its a really easy check up, usually you get an ultrasound, and your dr gives you a due date. Based on the information you gave your due date would be November 20th. You have a real live, developing baby inside. Life has began, your baby is still a baby right now, its just developing. Right now your baby already has all of their genetic makeup of whether they will become a boy or girl, what color eyes and hair they will have. Its so important to make a point to not miss a drs appointment when your pregnant because there are lots of medical things the drs check for: UTI's, pregnancy related diabetes, preclampsia, ectopic pregnancy, they check for a heartbeat, and check the babies growth. A lot of times a drs appointment can save your life or your babies in the event that something goes wrong. Take it from someone who would have died without getting to a dr very early on with my first pregnancy, It is way more important than people realize!!
Right now, your baby is already moving and in about another 8-12 weeks he/she will be large enough for you to be able to feel these movements inside of you. I am proud of you for choosing to be responsible and keep the baby. A lot of girls your age feel like they cant finish school or go to college. I know so many girls who did all these things with more than one kid. Some single, some married. So try to remember that you can still follow your dreams while allowing your child to be able to be born as well.