Here's what we did that worked. J started on Reglan early in life, he took 0.9? It was a very skinny syringe that went to "1" and his dose was just under that. He had the medicine about 15 minutes before every bottle. We added about 6 drops of simethicone (gas drops) to the nursery water in every bottle when we made them up for child care or shopping trips, they looked slightly milky but it was the drops. We never laid him down flat. He slept in a bouncy chair, it reclines slightly and when he moves it sways/jiggles/bounces up and down. We sat it in his baby bed and strapped him in until he started fussing and seemed to want to lay down, maybe 10/11months.
I don't know anything about Previcid as a med except it causes the acid producers in the stomach to not make so much acid. Reglan, on the other hand, causes the stomach to relax and that allows the food to go on out at the bottom quicker and less painfully.
Pharmasists know everything about med's, doctors don't know much. Talk to the pharmacists that filled your prescription about the side effects you are possibly seeing.