My son is on Prevacid for his Reflux. Please help?

Ok when my son was 2 weeks old he was diagnosed with reflux. They (pediatricians)put him on Zantac and i was also told to thicken his formula with a little rice cereal. Also they changed his formula to Similac Alimentum. The medicine did seem to help but not 100 percent, so then they put him on Prevacid which was like a miracle drug! It works soooo well for him. Ever since he was born he has been a very happy baby he barely ever cries, so when at 2 weeks he would cry or be fussy at feedings i knew something was wrong. Well now he is almost 11 weeks and the last few days he has gotten really fussy in the evening time. And it just dawned on me that it was probably his reflux acting up again. His breath and pacifier has been having this smell to it, kinda like a spit up/something else kinda smell don't really know. So when he had another fussy evening i called the DOC on call and he said to give him another dose which we did, now he seems to be fine. He gets a 15mg dissolving tab every morning. The DOC said to start giving him the 15 mg tab at night. I thought maybe half in the morning and half at night just to space it out. I guess what my question is has this happened to anyone else? Like did ur baby do great with the medicine and then have to be put on a higher dose? Maybe because of weight? My son is almost 12lbs. Please help!