I'm getting a little concerned, I know all babies development differently, some parts faster than others and some parts slower, but my little one is almost 4 months and still doesn't lift his head up when doing tummy time. We try and do it lots, and he's definitely gotten a bit stronger and can life it just to change sides. But can't go on his elbows or anything, I'm getting a little concerned. Any advice, tips? Iv tried using the pillow. Iv tried laying down with him on the floor, putting toys/mirror, even my phone with cartoons on it. But he just hates it and fusses the entire time without really trying to lift up. Any suggestions?!