Preemie w/Acid Reflux????

Hello, my preemie was born at 31 weeks on 8/6/08. She is now 3 months, adjusted age, 1 month. Early on, she experienced constipation and would not pass stool for 2 days at a time, she was given prune juice to help with that. She used to get breast milk exclusively until my supply got low, now I supplement with Similac Neosure (s special extra calorie formula for preemies), she is not getting more formula than breast milk. She now has these periods where milk will come from her nose and/or mouth and she seems to stop breathing, she gasps for air and cries. I use the buld syringe to get the milk from her nose. She just started waking up crying as if she is jolted from her sleep and is in pain. She grunts alot and moves around. I have her sleep on an incline, which helps some and after each feeding I keep her inclined for at least a half hour laying chest to chest to aid the digestion. I would like to know if there is anything that will not harm her delicate system, but will help alleviate or even get rid of what she's experiencing now. She also a liquidy dark green stool.