It is possible that you have a very forceful letdown and it is spraying the back of his throat too hard. This is common in the first few months of nursing, especially with the first child. (Also you have not been nursing and maybe your breasts are very full) One way to help this is to cause your milk to letdown before he nurses and let the pressure reduce a bit before you put him to the breast. You may only need to let the milk letdown and spay or drip for a few seconds, or you may need to express some of the milk out first, in order to reduce the pressure. It depends on your particular breasts and baby. If this isn't working, try expressing a very large amount of milk from the breast or even try to empty it as much as possible and then nurse him. If you are still having trouble when the breast is empty, then letdown would probably not be the issue. It could be that he is not latching correctly because he is used to a bottle nipple and the end of your nipple is hitting his throat. This is all the help I've got on this. I hope it helps!
Good luck and hugs to you!!
Good luck and hugs to you!!
