A proper assessment of your symptoms is warranted. While your MRI will reveal the affected sites, these have to correlate with your clinical symptoms.
Typically pinched C3 and C4 level spinal nerves should not lead to spasms as these do not supply big muscle groups in the neck.
Treatment for such symptoms are generally
1. Medication. Simple analgesia may help with painful periods. If your pain is neuropathic (nerve like pain), then anti-neuropathic agents such as gabapentin may be helpful.
2. Physical therapy. This includes physiotherapy and generally allows for greater spatial awareness of the neck and shoulder muscles. At the same time, prescribed exercises will strengthen weakened areas. Passive physical therapy includes massage, acupuncture etc. These, if helpful, will provide temporary relief.
3. Intervention. Considering the extent of pathology, you may have had a surgical consult. While there is a role for surgery ( you will require a proper assessment and consultation if this has not been done), pain intervention may be helpful.
These range from simple trigger point injections to help with muscle tightness, to xray-guided procedures to direct needles to specific parts of the neck bones (cervical vertebrae) to deposit therapy.
Do discuss these options with your friendly orthopedic surgeon or pain physician!
