It has been three years since a rotator cuff injury, and sudden sharp pains occur when exercising. Do I require surgery?

Rotator cuff tear. Not necessarily. First a repeat MRI has to done to determine if there is a tear and how extensive it is. The MRI should be done with a dye injection(gadolinium ) in the join since you have had prior surgey. A small tear may improve with just physical therapy.
Mri First. Mri arthrogram to see if you retore the repair no push ups no military press after rotatorcuff repairs they are not all fixable you might consider playing defense.