Welcome to MDC! I was 18 when I got pregnant with my first, it's exciting but dizzying isn't it? I read all I could get my hands on, and went to a Bradley Method class with my hubby near the end of my first one. It helped a lot to feel on top of everything better.
For the stomach pain: Chewable DGL Licorice, find it probably at a health food or supplement store, or buy online. Especially good if it's a heartburn thing. For the gas try Simethicone gas relief capsules. See if some foods make it worse and avoid those. Are you having food aversions and nausea, too? That can make it hard to eat healthy. A high protein diet with very little refined flour and lots of veggies and some fruit is ideal but if you get nausea badly of course just eat whatever you can eat. Maybe if you're open to it you can post what you've been eating and we could suggest a meal plan to help you feel better.
It's easiest to get to sleep in a totally dark room, especially no blue lights from electronics and a heavy curtain on the window. Use lots of pillows to support you just right. Read fiction before bed maybe, or have your boyfriend give you a massage, or if you pray then spend a long time doing that. Don't watch tv right before bed.
As far as the mood swings, try to be lighthearted about it "oh there I go again, goodness I'm so pregnant". For stuff that brings out deep seated feelings go ahead and express those and explore them. Perhaps you can use an artistic outlet, sketching or painting, poems, journaling, photography, music, you don't have to be great at it to express yourself. Give a name to your worries, don't let them be vague fear figure out what you're concerned about and what you can do about it, and whether it's something worth worrying about at all.