Muscles of my face hurts... what could be the possible reasons?

Facial muscle pain: Causes likely include overuse, such as chewing tough meat or gum, or trauma or stress from heavy exercise. If the muscle pain includes other areas of the body, and doesn't resolve with rest, systemic problems, such as myosotis, should be evaluated by your physician.

Grinding: You may be clenching or grinding your teeth, leading to over activation of the muscles in your face, neck and head. You need to have an evaluation by a dentist.

Muscle soreness : is a post-exercise muscle pain that may result from excessive workouts. Presenting symptoms include muscle weakness, palpable tenderness, and pain with active muscle contractions. Symptoms usually subside within a short period of time without any residual effects. Rest and drink a lots of water, moist heat, eat soft diet and NSAIDs OTC to remove inflammation and pain. See orofacial pain specialist