Milestones.. questions

My baby will be 8 months tomorrow! He isn’t crawling or rocking on his hands and knees quite yet, he doesn’t say mama or dada, and he can sorta sit on his own but ends up really leaning forward or arching back to where he would topple over if I’m sitting behind him he does okay. A friend of mine told me he seems really behind and that I should be concerned and to call his doctor?? He has an appointment next month.. I didn’t think I needed to be concerned yet..? Do I really need to call my pediatrician before his next appointment?? I worry about everything and she knows this, so telling me this has me overthinking everything.