Thanks for your question on Healthcare Magic.
I can understand your concern.
In my opinion, possibility of
musculoskeletal pain is more.
But since it is from long duration (3weeks), better to get done chest
x ray to rule out lung pathology.
If chest x ray is normal then no need to worry for major lung diseases.
Musculoskeletal pain is more likely.
So take painkiller like
ibuprofen.
Avoid movements causing pain. Avoid bad postures in sleep.
Avoid heavyweight lifting and strenuous exercise.
Apply warm water pad on affected areas.
Don't worry, you will be alright.
Hope I have solved your query. I will be happy to help you further. Wish you good health. Thanks.