7 month old can't put weight onto legs?

i don't know if i should be worried or not, i know they say every baby is different and reaches milestones at different ages but my 7 month old cannot bear any weight on his legs, he just flops down like a noodle. he can bounce in his bouncer though and roll around the floor but any time you try to stand him up or even gently put his feet on the floor his legs kind of cave in? He just learned how to roll and is eating solids twice a day. Can't sit unsupported and only recently started babbling. Just wondering if any other mamas have noodle like babes? Edit: would also like to add that he tends to shake quite a bit too, especially in his arms.