Possibly rotator cuf. Most common shoulder pain is overuse causing rotator cuff syndrome which ranges from mild tendonitis to complete tear. You should get complete clinical evaluation and possibly xray and/or MRI depending on exam findings.
Why? There has to be a reason. What are you doing to it?
Get evaluated. Severe shoulder pain could have multiple causes including infection, nerve compression, overuse, trauma, and even a neoplasm. A physical examination and diagnostic imaging will likely be necessary.
See orthopedist. Shoulder pain can be referred from the neck or it could be locally from the shoulder. Common local problems include but not limited to arthritis, bursitis, impingement, rotator cuff tear, labral tears, biceps problems, stiffness, and instability. Common volleyball related issues are: instability, biceps and labrum problems in addition to partial tears of the rot cuff. See a shoulder orthopedist.
I've had a pain in my shoulder for some time. Some times it will radiate to my hand, others in my arm pit. My shoulder its always sore and feels almost like it needs to pop and stretch and be pressed down hard at the same time. It's the most frustrating
Get some PT. Sounds like you need a doctor exam for rotator cuff strain and a course of physical therapy combined with some Naproxen. If not improved afterwards, then an MRI. TRIGGER POINT INJECTIONS could also benefit. Have your doctor palate your trapezius from neck down across your shoulder, your supraspinatis, and over shoulder blade for discrete tender spots.
I have numbness in my arms and hands, weak neck, I pull muscles there easily. My left shoulder blade is always sore.
Be seen. I would certainly be seen and have further testing including possibly an MRI of your cervical spine. Your symptoms could indicate compression of your spinal cord in your spine.