Worried

So yesterday my son had his 6month check up and immunization. He's 6 months and 3 weeks and doc is concerned that he is not meeting his developmental milestones such as sitting, standing , rolling. She also mentioned him having low muscle tone and referred us to a neurologist. I'm trying not to freak out and jump to conclusions but its hard not to. Has anyone else gone thru this? Lazy baby syndrome maybe lol? He hates tummy time and I really haven't pushed him so I'm hoping its just that. Will definitely push tummy time now until we see neurologist 😕