Thank you very much for the useful information.
This looks more like a muscle spasm secondary to the trauma and its resultant muscle damage.
In general, this usually settles down in few days to week.
You are taking a muscle relaxant --- its good, but please note this is not simply a muscle spasm. This spasm is result of muscle trauma and inflammation and hence you need anti-inflammatory medications as well such as ibuprofen or naproxen.
These will reduce the inflammation, as well as pain and will reduce the stimulus for the muscle spasm while you continue with the muscle relaxant.
There is remote possibility of a bony fracture as well, which can only be ruled out with the help of an X-ray, but honestly this seems more like a spasm, nothing else.
You should also apply heating pads over the affected are.
Maintain adequate hydration and nutrition.
And Motrin or Aleve should be taken.
See how you respond to these measures in next few days.
If the problem persist, does not improve or gets worse, see your doctor for a clinical examination and further investigations.
I would have been worried too if I were at your place, but let me reassure you that this does not sound serious at all. It is a treatable condition and carries a good prognosis with appropriate management.
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