Hi Nikki

This must be so overwhelming for you, but I'm glad you're reaching out. I'd say the best place to go to get your questions answered (other than here, of course!) is a doctor's office. You need to be followed from the beginning by an OBGYN or midwife. Prenatal (pregnancy) care should start right away, and your doctor/nurses will be able to give you a very good idea of what to expect and what's normal.
Please forgive this next part if I'm way off the mark, but at your age you should probably also be asking yourself (and give yourself some real time to decide) if you _want_ to become a mother. My first pregnancy was a surprise and way younger than I wanted, and I never really gave myself the opportunity to look at the choices. Family especially all acted as if I'd be insane not to keep the baby--my mother was crazy high-pressure. In hindsight, I think it would have really paid off to look at the adoption option. I was never comfortable with the idea of abortion, but now that I'm older and have friends that have adopted (plus friends that have given babies up for adoption), I see how beautiful it all is. In fact, I found out last year I have a half brother (my father's son, conceived when Dad was in young and in college)--he was given up for adoption at birth. It's a lot more common than you might think!
Anyway, not to turn this into a novel, but give yourself some time to figure out the path that's best for you and the baby. There are so many choices, so many ways to be happy....just remember that, okay? I remember how panic stricken I was and how trapped and overwhelmed I felt, and now looking back it didn't have to be that way.
Oh--and the line on your tummy is the "linea negra." It shows up during pregnancy, darkens a bit, then goes away in the months after birth. Totally normal and nothing to worry about.

The tiredness and stomach ache should go away at the end of your first trimester, at about 13 weeks or so. Sometimes it takes a little longer, but for most people it _does_ go away.
I hope I didn't offend you in any way. You've found a very supportive community of women here, and I know everyone will try to help. You are _not_ alone. A lot of women here are/have been young mothers, and I'm sure you're going to find a lot of support. Hugs, sweetie.