Hi, My Baby Is 4 Months Old And Weighing 11

Hi, my baby is 4 months old and weighing 11 pounds. She is having acid reflux and so she is taking Zantac 0.6 ml twice a day. She used babble and speak a lot but for the past 3 weeks she is not cooing or babbling , she seems to be very silent but a happy girl. I'm really concerned about this, is this something to do with the reflux????