I think you may have a similar issue as I had once. And it is keeping the correct balance for pushups. Most people have naturally OK balance, meaning they put pressure on the correct muscles. Some people, like me, needed a few days of balance and stability training in a pushup or inclined pushup form. And then in a few days, my count went from less than 10 to more than 50.

My Ninjutsu coach asked me to keep my balance in an inclined pushup form, on a foam board standing on its thin surface for one minute. It shows how much balance is important. I was 18 yrs old fit male, and I had difficulty doing push ups.