J.B.
If he's gaining weight, don't worry about it. Some just don't like the bottle. Mine never took one. I take care of another one since she was 6mo old, and it took her a while before she got used to the bottle. Then she had no problem. She was also eating gerber baby food in between bottle and breast. And she did just fine like that. Now they are both almost 18mo old and both are healthy weight.
Try different bottles until he likes one, but not from you. Have your care-provider do it.