My son was born wen i was 33weeks 4days.

Babies often swallow air during feedings, which can make them fussy. To help prevent this, burp your baby often. Try burping your baby every 2–3 ounces (60–90 milliliters) if you bottle-feed, and each time you switch breasts if you breastfeed. If your baby tends to be gassy, has gastroesophageal reflux, or seems fussy during feeding, try burping your little one after every ounce during bottle-feeding or every 5 minutes during breastfeeding. Try these burping tips: 1- Hold your baby upright with his or her head on your shoulder. Support your baby's head and back while gently patting the back with your other hand. 2- Sit your baby on your lap. Support your baby's chest and head with one hand by cradling your baby's chin in the palm of your hand and resting the heel of your hand on your baby's chest (be careful to grip your baby's chin — not throat). Use the other hand to gently pat your baby's back. 3- Lay your baby face-down on your lap. Support your baby's head, making sure it's higher than his or her chest, and gently pat or rub his or her back. 4- If your baby doesn't burp after a few minutes, change the baby's position and try burping for another few minutes before feeding again. Always burp your baby when feeding time is over, then keep him or her in an upright position for at least 10–15 minutes to avoid spitting up.

consult pediatrician if not improved with above tips