This may seem a bit advanced for a 20 month old baby but I'm thinking longer term when you need to focus on potty training. If you can give the child a heads up of what's going to happen (we need to change your diaper) and also of what will follow after that (then we can have ice cream / go outside to play etc). It is a First > Then principle they teach in ABA and it helps the child transition through a unpleasant task onto something more rewarding. Also the child could be sensing your displeasure with this not so pleasant task so calm, soothing reassurance from the parent is required.

Mine is 4 now and still in diapers, sometimes he won't allow me to change his diaper but in ABA we are working on first, then principles. This works. I take his iPad, and Say 1st, diaper, then iPad. This is a last resort. First I ask him to come lie down so I can change him, he usually does after I ask him several times. For a 20 month old though, I am not sure if this will work. But over time if you keep taking the toy that he likes best away, then keep repeating, diaper first then toy....over time he will get it and comply. But do not five him back whatever toy/object he has until he complies and allows you to change him. It may seem quite harsh but it works.
I can't say enough good things about ABA therapy. Learn it, live it, use it. It works.

Success! We got a basket and about 15 toys from the Dollar Store. This morning was the first time trying it. I allowed him to pick a toy before the change and he didn't make a peep or move after that! The toy went back in the basket when we were done so it's there for next time. Hoping this new technique continues to be successful!.

My daughter is a little better now then she use to be. I notice she is worse with diaper changes if she is busy doing something and doesn't want to have to stop. I try to wait a minute and tell her and that helps. I also try to distract her with a toy or sing if she is trying to get away. Hope your toy basket keeps working for you!

Hi there.
Same problem here.
I ordered a book that someone recommended.
Not particularly about diaper changes, but it had a piece.
First, change in the same place every time. We were and are still guilt of changing in the couch as well. It's safer at this point.
Second, is your little one sensitive to light? I've started turning off the light and it seems to help.
I also have started to tickle him when I lay him down to change him.
Sometimes these things help, sometimes not.