Three Month Progress

I was just seeing where different babies are/were at at three months??? My son still can't really hold himself up during tummy time or even sit up that well, he holds his head up great when I hold him but other than that, nothing... I try so very hard not to compare him to other babies, that is one thing I promised I would not do to him and just let him progress at his own rate of comfort but right now, I'm just curious as to whether his.. Stage in said progress is normal.