HELP I need advice

A little backstory my oldest son is 4yrs old and has autism. My youngest son just turned 9 months old and I feel like I’m doing everything wrong! He just had his 9 month check up today and when she was reading the list of milestones he’s barley hitting any. He can barley sit up unassisted, he doesn’t crawl, he doesn’t babble, he cries ALL day (he is teething which could be the reason for that) I don’t know what to do I’ve basically cried all day since we got back from the appointment. Since my oldest has autism I’m so so scared my youngest has it too. I need advice I need to get him to reach his milestones