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Congratulations for the baby. Well, I got your concern. It may be due to GERD (gastro-esophageal reflux disease). Do as I say. Do proper burping after each feeds, minimum 10 minutes. Make him sleep in somewhat high head position 10 to 20 degrees maximum. Watch for his weight gain. If he is not gaining weight then consult a pediatrician. Many time these things can be controlled with simple measure only. In some cases, we need to give Lanzoprazole but for now, let us wait and watch.