Thanks for your query.Based on the facts that you have posted it appears that you have sustained injury to your back due to fall from horse .Since then you are getting pain in back and abdomen .
Since you do not have hematuria ( Passing blood in urine ) it is most unlikely to be kidney injury.
Please consult qualified general surgeon
for clinical examination most likely it looks likely that you have muscular pain
due to blunt trauma
Please take anti inflammatory medicine like Diclofenac
twice daily will pain killer like Brufen
I think it will get cured within a week.