I was 21 when I had my first daughter and I were all those things minus a boyfriend. You are fortunate to have him around, you'll both need each after baby is here. Motherhood didn't come easy for me, for I was depressed all the time about not having a daddy for my daughter. I am now 39, she'll be 19 this Sunday I got married when she was six, had two other girls, and now 34wks preggo with my first boy. Continue to believe in yourself that you will make a great mother. Love is all they need anyway. Blessings to you.
Make sure you're comfortable with your doctor/midwife. You're going to see them an average of sixteen times in the next year so switch now if you aren't comfortable. Don't be afraid to ask questions.
Research all different kinds of birth (completely "all natural" homebirth up to a planned c section) and decide what your preferences are for everything. (Would you rather have an epidural? A water birth? Be induced our let baby choose his/her own birthday? Etc)
Once you know what you're leaving toward make sure your provider respects that and can help you achieve it. Ask specific questions about c section and episiotomy rates, vacuum and forceps rates, etc, especially if avoiding intervention is important to you.
Feel free to message me any time. I'm also 21 but I'm expecting my second!