He ain’t crawl or anything :/

Should I talk to his doctor? He’s almost 8 months and he’ll sit up if I get him up but he won’t on his own. He much prefers to lay down on his back and he won’t do tummy tiny no matter how much I try to make him do (which is every day!) he won’t crawl or sit up for a long time (he’s a little chunky but I wouldn’t say TOO chunky) and will kind of stand if we hold him up but he won’t dare move his legs or bend them. I’m honestly a bit worried because I know other babies his age already picking themselves up and crawling everywhere and he doesn’t seem to want to at all :/

What should I do?