Why do I have shoulder pain after doing push-ups?

Since I began doing pushups, I've noticed a sometimes-dull sometimes-sharp ache in my right shoulder when I’m going about my day. What could this be from?
I recently started working out more frequently, doing 3-5 hour long yoga sessions every week and trying to build arm strength by doing 30 push ups (with my knees down)…

Why do our arms hurt when we do push ups? - Quora

Why do our arms hurt when we do push ups? - Quora

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Why do I have shoulder pain after doing push-ups?