Not sitting up :(

Anyone else having issues? I feel like he's so behind on milestones. He's rolling around, acting like he wants to crawl, wanting to stand all the time, also no teeth poking through (maybe starting now) - but he doesn't want to sit up. He hates it. I know all babies are different and they all go at their own pace.. but I see babies that are in a whole different category (months younger) that are sitting up, standing by themselves, teething.. obviously I can only do so much and it's up to him, but damn he's stubborn 😂