Hi,
I really understand your concerns, but what you describe overall does not sound like the typical autism red flags. However, autism is a spectrum disease and no kid with autism is alike. Definitely continue down the road with getting appointments and go to the one where you get in earlier. Also tell the doctor's offices that you are a SAHM and that in case they have a cancellation, they can call you anytime and you can come on a very short notice. That usually helps with getting an earlier appointment.
Meanwhile, start setting up playdates with kids his age and see how he does in these. Work with him on sharing toys (even if he just has to share them with his teddybear, or you) and also start other pretend games, like saying hi to the teddybear. Whenever you meet strangers, you have to first be the perfect example of how to greet and interact with strangers and then make him interact with them, too. Make him say "hi" or wave at least, even if you have to go to him, pick him up, go to the stranger and then encourage him to say "hi" or wave. This can also mean that in the beginning you have to guide his hand for the waving. It is getting warm out, go to the playground every day and try to encourage interacting as much as possible.
For speech, also encourage him to speak as much as possible. Make him say "up" (or an approximation, not just screaming) if he wants to be lifted up into your arms. Make him say "milk" if he wants his milk. Don't get discouraged if he doesn't say what you want him to say right away, just hold on to what ever he wants for 20 - 30 seconds. If he says the word, praise him, give it to him right away and repeat the word. "Yes, milk, that is your MILK, good job, here is your milk".
It is your job to model the right behavior and the correct speech from now on. Once the speech therapy starts you will see the therapists doing a lot of the same thing. Try to learn as much as possible from them.
Oh, one more thing. Get Baby Bumblebee DVDs! They are great for kids to learn to speak and increase their vocabulary and they are made for this age group!
Good luck!