Thanks for your query.
1. The pain which comes on yawning and deep breathing and which also comes on touching locally is a local muscle or soft tissue injury
related pain. You definitely need to give rest to this part. Application of a moist heat (towel wet with warm water) will help. If the pain persist consult your physician for medication.
2. Mostly this happens when you subject your untrained muscles to excessive work. So always try to build up your work load gradually. Hope you will succeed in your aim.