Sounds like tummy time problems are pretty common. My bubs JUST started kind of liking it, like literally in the past couple days. He is 3.5 months (almost 16 weeks).

Just wanted to add my other favorite variety of tummy time position, and I hope I can explain this right.... you lie on your back on the floor with your legs bent 90 degrees at the hip and at the knees (so the lower part of your legs is parallel to the floor), and then rest your baby tummy down on your shins facing you and hold their hands. Their head extends beyond your knees so they have to hold it up, but they can look down on you- my baby thinks that's HILARIOUS. Requires a bit of balance, but I manage it with a 7kg+ baby, so it can be done!!