Welcome at HCM.
I have read your question it looks fom your details that you may be having sacro iliac strain.The sacro iliac joint is joint at the junction of hip with spine.
You should do following to have relief in this-
-Avoid forward bending at your back.
-Do complete bed rest
for at least 3-5 days.
-Do warm fomentation at affected area.
-Apply a brace like lumbo sacral belt.
-Take a good analgesic
on your doctor prescription.
-Take the help of a physiotherapist.
Hope this all will help you.
With best wishes.