I have prescribed medication for pleurisy and now I am stiffer and weaker than normal and I am not sure if it is the medication or the pleurisy?

Pleurisy. I am skeptical of a diagnosis of primary pleurisy as, in my experience, pleurisy is usually a component of pneumonia or part of an autoimmune disorder. I recommend a second opinion regarding your diagnosis and treatment.
Medication. It will depend on which medication you got. Cortisone is often given as part of the treatment, and can be the cause. It should disappear in 4-6 weeks.
Consult. Please consult your GP. You will need a chest x-ray.