It may be gas like you mentioned before. Many babies cannot tolerate dairy, and if maybe you have been eating it try and cut it from your diet to see if that helps. My daughter was a very gassy child too, and she was given formula from time to time when I could not nurse. We switched formulas 3 times, and I cut much of the dairy from my diet and it worked wonders once we found the right formula! She ended up taking to Nutramigen the best, but we did try Gentlease first.
If she is teething, you will be able to tell by extra drooling and by running your finger along her gums (the front bottom 2 teeth are usually first, but not always!) if you feel little bumps or swelling, there ya go. Oragel works wonders, or homeopathic teething tablets work well too (or so I am told, I haven't tried them! I don't remember the brand name for them either, ask around)