Wiggling while feeding

I am a STM with a 14 weeks boy. He is doing paced bottle feeding because of gas issues, so he is taking the bottle in lateral lying position. Since the last few weeks feeding has been a real challenge, as he is wiggling,kicking, rubbing his ears, pulling his hair. He is not crying and his appetite is pretty good. I really find it difficult to keep the nipple in his mouth. Can you suggest what the reason may be or how can I handle the situation.. Thanks!