Uy, first time mom din ako kaya naiintindihan ko ang worry mo! That upper stomach pain you're describing, especially near the ribs, is actually pretty common in early pregnancy kasi lumalaki na ang uterus at nagsisimula nang mag-adjust ang lahat ng organs mo, plus the ligaments are stretching na. The fact na nawala siya after you changed position and may gas relief ay actually a good sign, sounds like ligament pain or gas which both happen a lot sa pregnancy. That said, since this is your first time at gusto mo ng peace of mind, I'd really suggest mentioning it to your OB sa next checkup or mag-call na lang if it comes back ulit or may ibang symptoms, better safe than sorry talaga, especially pag first time mom ka pa lang. A few of us mums had similar experiences at okay lang naman, but your doctor should be the one mag-confirm na lahat is normal sa case mo specifically.