How can I help my son lift his head?

My son is a little over 2 months old. I've been giving him plenty of tummy time but no matter when I put him on his tummy he won't lift his head. He either just lays there and coos and moves his arms and legs or he falls asleep. It doesn't matter when I try to do it he never lifts his head. I've tried after naps so he won't falls asleep. I've tried in the morning, afternoon and evenings a few times a day but he just won't do it. I know his neck is getting stronger because when I hold him up he can hold his head steadily and can look around with ease but I'm getting concerned because he won'tlift his head at all when he's on his belly. Is there something I can do to maybe help teach him or something? Please no rude comments.I'm just concerned because how is he ever going to learn to crawl or even roll over if he hates to be on his belly so much and won't lift his head. Has anyone else ever had this issue?