Concerned about development

Hi everyone, my son was born via csection at 37 weeks due to cholestasis. Over time I’ve felt he may be a little delayed. He’s now 11 weeks and doesn’t really lift his head during tummy time. He just lays there like it’s nap time. He won’t look at or reach for toys when he is on his back on his play mat. His hands are still in fists mostly. He’s constantly staring more at the pictures on the walls than he is me or my husband. He smiles and squeals but we really have to grab his attention. He does have one of those sit me up chairs and really enjoys being in that though. I broke down last night crying to my husband about it because he’s just so far behind compared to how our daughter was. I know every baby is different, but I’m just curios if anyone else is in the same boat. I was told by his doctor to do some of his milestones by due date because he was 3 weeks early but he should mostly be “on time”. going by due date, he would developmentally be 8 weeks. But even looking at those milestones, he still seems delayed