She cries to keep herself awake.
If she is crying when trying to sleep it is her way of telling you something is wrong. It may well be she is tired but wants to be held because she cant settle herself right now, or it could be she is OT and cant shut out the stimulation.
Is her cot elevated? Do you use white noise and a dark room to help shut out the stimulation? Dummies are also really great for reflux babies and help with keeping the milk in the tum, minimizing crying (which gives them more wind/gas) and helping them settle to sleep.
How far apart are you giving the prevacid and zantac doses and what is the dosage she is on?
You will have some days where you just have to hold her....esp bad reflux days...BTDT and it is hard, but it does get better