Not sitting by himself yet

Araceli

Hi everyone! My LO is 7 months and will be 8 months on the 30th and he's been crawling for almost a month now and recently has been walking in his walker pretty good not so much forward yet but sometimes he will but cant direct himself. Anyways, he's still not sitting up by himself yet. He will for awhile and then he just falls over if he tries to reach for some thing or gets too excited. Is it normal that he doing other things and not this?