Hello, sorry you are going through this. It sounds similar to my neck dissection in early 2017. My SCM was partially cut because it had been punctured to reach the lump during the surgical biopsy. I am not aware of any muscle relaxers for your situation but if I were in your shoes I’d be trying them, like you are. For me what has helped the SCM tremendously has been laying on the affected side and stacking pillows under my head. It stretches the SCM on that side. My SCM really liked being stretched and I would find myself regularly tilting my neck to feel the slight pull on the SCM. Later on I got massages for the neck and they helped but the best therapy I could do every day was with the stacked pillows (I normally sleep on the other side just because I have my whole life but each night before falling asleep I would do the pillow stacking stretch for 10+ minutes on the affected side.
Regarding the shoulder, I also have problems (my accessory nerve was cut). They will have you stand near a wall and use your fingers to crawl up the wall in order to lift your arm at the shoulder. This can work even better with a warm wash cloth or wet heating pad on the affected shoulder.
My suggestion would be to discuss your return to work with your oncologist and physical therapist. Sometimes surgeons can be overly optimistic with their recovery projections (and in my case the surgeons only wanted follow ups every 3 months (or less frequent if I hadn’t been persistent).
With 55 lymph nodes removed (I only had 44 removed) you may also want to get a mini trampoline 3’ diameter (“rebounder” for $30 on Amazon). Lightly bouncing on this 5 min per day can get your lymph fluid moving and reduce any fluid buildup (swelling) in your cheeks and neck.
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