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)…

How to Fix Wrist and Shoulder Pain From Push-Ups and Planks

Elbow Pain During Push-Ups (A Helpful Guide)

Are wide pushups bad for you?

Push-Ups Feel Impossible? Start with These 4 Beginner Progressions

How (And Why!) To Do Push-ups

Why is it after I do push-ups, my back aches the following day? It

How to Do Pike Push Ups: 13 Steps (with Pictures) - wikiHow

6 Push-Up Variations to Build Strength and Improve Shoulder Health

11 Exercises for Arm or Shoulder Pain During Pushups