Baby/toddler says words, stops saying them, then it comes back a month later?

Question

My son is 19months old and has in the past said words like mama dada, stopped saying them for a month or two, then will say them again. Currently he has learned new words so some of his other words are not said as much. 
I’m worried because I know of two moms whose said their child having a “roller coaster” - up and down, vocabularies was one of the signs that lead to their sons autism diagnosis. My son doesn’t show any other textbook signs of Autism but it still worries me, so I’m hoping I’m not alone with my child doing this and still being normal/ok 😬🤞🏼🙏🏼 
Speech seems to be something thats hard for him. He knows uh oh but the oh part is hard for him to do so it’s mostly just uh uh. When he was younger everything was “wow” and he doesn’t say it much but I also don’t think he’s encountering anything to where he would say that. He’s said “ hi dada” once in the car with my husband in response to him saying “hi (babys name)” . He’s said book maybe 3 times, said Apple once. Doesn’t say no but physically shakes his head. I’ve tried teaching him sign language and he knows all done, he learned the sign more and did it for maybe 3 days and now will not do it, yesterday as I was doing the sign, he grabbed my hands and had me continue the sign for him to get more crackers. That worried me a little but it’s a one time thing so I’m not gonna count that as him “using my hands to do things for him”. 
He says yeah, his new thing is “ I did it!” And he’ll raise his arms in the air, it’s pretty cute, but not always super pronounced where it’s obvious that’s what he’s saying to others. He’s also learned light and will randomly point out our house lights throughout the day. 
He says mama and dada, not all the time and the pronunciation isn’t really improving but he does say it and knows that the word means me and his dad. 
I’m just curious if any others peoples kids have done this “rollercoaster” of speech without being diagnosed with Autism or any other kind of developmental concern/issue.

Answer

My almost 5 year old seemed to do this with his speech.  He started to say little things, then it’s almost like he just decided speech wasn’t for him.  He had a handful of understandable words until he was 2.5.  At 2.5 he all of a sudden just started talking like he had all of the words in there the whole time.  As long as they’re understanding the speech you’re saying to them, that’s the biggest thing.  Some babies just start talking later.  My oldest was talking shortly after 1, it was crazy, then for my second to not say much at all until almost 3 had me so concerned.  He’s almost 5 and doing fantastic in pre-k now though.  No external diagnosis other than an expressive speech delay.  We did speech therapy for months and honestly it really didn’t do much, he still developed at his own pace.  If baby’s not showing any other signs of autism I would try not to stress too much on it☺️ The main advice my dr gave for our youngest was to read lots with him and talk to him as if we expect a response even if he doesn’t give it.