From your description, it sounds like you may have something going on inside the shoulder that should be evaluated before doing exercises that might make it worse. Impaired performance with decreased velocity, early fatigue, and loss of control are often the symptoms present when there is a rotator cuff tear and/or a labral tear.
You probably know the rotator cuff is a group of four muscles that surround the shoulder and allow it to move in all directions without dislocating. The labrum is a rim of fibrous cartilage around the shoulder socket. It is designed to create greater depth in an otherwise fairly shallow socket. The labrum helps aid in maintaining shoulder stability.
Overuse with repetitive overhead throwing at high velocities can lead to tears, damage, and other injuries to these soft tissue structures. Pain, clicking, and weakness are the most commonly reported early symptoms suggesting a problem. But the type of impaired performance you described is also a warning flag.
Early evaluation and diagnosis is advised. You will want to avoid stressing the shoulder even more until you know what’s going on. This could be a simple problem for which exercises are helpful. But exercise is not recommended until you’ve been examined and possibly had some X-rays or more advanced imaging. Talk to your coach and see your team physician as soon as possible — certainly before practicing or playing again.