We had this problem when my son was a newborn. We noticed that he drank very well from the bottles that the hospital sent home with us, but those ran out fast. So, we tried to find something with a similar nipple. In the end, we tried almost every shape in silicone and latex. And I don't know if he just eventually got the hang of it, but he did finally take to the Avent bottles. You can try positioning his lips for him, the nipple needs to be completely in the mouth and his lips should be around the fat part at the bottom.
