Hey girl,
First things first, good for you for reaching out and asking for help and advice.
Second, noone, and I mean noone can tell you what to do, but this is one serious situation. You have made a dicision to grow up very quick. You have made a decision that will affect yours and this baby's life for ever.
The only advice I have is to hang in there. Get that ultrasound, let me tell you it is the most amazing thing. You have a long road ahead of you, but there are people there for you. There are people who will listen and talk to you.
I am 21 now with a 14 month old little girl and am 7 months pregnant. I know getting pregnant at 19 is far different from getting pregnant at 15, but I was young and lost as well.
I am now happily married, but it was a long hard road and totally worth it.
Don't worry, you'll get through it.
Two other things, you should definitely find a doctor or midwife that you are VERY comfortable with and whom you like a lot. This person will be with you through you're whole pregnancy so don't be afraid to ask anything anytime. That's what they're there for.
Also, find a Doula. They are amazing people. They are Labor Couches and they help you through your whole labor and birth. They are wonderful, caring, beautiful people. There are ones out there that will do it for free. Call around.
Last but not least, keep your chin up. No matter what anyone tells you or says to you, you are an amazing person going through something a lot of women wish would happen to them. Just stay positive and don't give up!
~Melissa