OTC liquid antacid for infant??

I was texting my sons pediatrician about him crying when trying to nurse. She thinks it's his reflux acting up and said until she can get us a different prescription, use 1/2 tsp of an otc liquid antacid. When I asked her which one she hasn't responded. Does anyone else do this?! What do you use? My son is only 13 weeks so I am surprised she suggested this. But he isn't eating well and is having a very hard time sleeping.