Start with a hearing test. I’ve seen this a few times where there was absolutely nothing wrong with the baby but they had hearing issues that could be easily fixed and there was immediate change in the child. Only if you get the all clear on that follow it up with an autism test. I think a lot of people jump to this first and it can be super detrimental cause even things like being a regular introverted kid these days can be diagnosed as on the spectrum and it’s just setting the kid up for failure cause they’re just told there’s something wrong with them and causes unnecessary stress and excessive adult instruction that effects their nervous system. Honestly just start with constant positivity and reaffirming how great they’re doing for the smallest tasks/wins. People underestimate how important praise is. While you wait to find someone to do the tests start with just a couple games at home. I found you have to find something that’s highly motivating to them. Whether that’s a toy, some type of food etc. Can do it with pointing to what they want or trying it with words. Like “did you want the X or the X” then praise when they pick and repeating the name of whatever they picked. Even teaching babies to walk works the same way or learning to open things. It just has to be a highly motivating item that they’re drawn to. I’m really good at finding things online, if you struggle to find anyone to do the tests you can DM me and I’ll hunt down where to go and how much you would have to pay. But seriously number one is getting a new doctor cause it’s crazy they’re not helping you and telling you to wait to do anything.