Random Flare Up?

My daughter was born 4 weeks early at 5 and a half pounds. She was diagnosed with GERD at 2 months, and was put on Zantac. After having to hold her over my shoulder after every feeding for 45 min., finally at age 3 months things seemed to calm down. Now, at age 4 months, the reflux has returned and is actually worse than when she was diagnosed. She is still on the Zantac and I am still avoiding dairy products. Is reflux suppose to worsen at 4 months old? Or could there be another problem? She is constantly making a grunting noise and will only eat for a few minutes every feeding. She is also constantly chewing on her fingers, which she didn’t do before. She only naps a max of 45 min and is now waking up every 2 hrs or less at night. Help!