For the past 4-5 days I've been having left shoulder
Probably Ligamentous injury inside the joint.
Hi I am Dr Gopal Goel Orthopedic Surgeon.
The way you have described the problem, there is a possibility of ligamentous damage inside your shoulder joint. I suggest as a first step you get a X ray of the shoulder joint.
In the meantime , start pain killers , muscle relaxants and local heat + physiotherapy.
If the X rays are normal and you do not have any improvement in about 10 days , then MRI of shoulder joint may be required.
Thanks and please feel free to ask any other question.