Hello and Welcome to ‘Ask A Doctor’ service.
I have reviewed your query and here is my advice.
Slamming down on a had surface causes many types of injuries and some of them may get well, some linger on or increase with time as no one takes
bed rest.
The pain in the back the way you have explained looks to be due to muscular only as it is increasing with bowel movements, making movements difficult and you have not mentioned about any
referred pain to the lower
limbs or so.
This can be very well diagnosed by a clinical examination, evaluation and if required by a an
MRI of the affected area.
Till then do the following:
Take a full bed rest.
Take an anti-inflammatory medications like
Ibuprofen if ti suits you.
Apply local rubefacient liniment.
Take a Laxative for soft and smooth motion.
Hope I have answered your query.
Let me know if I can assist you further.