What kind of treatment can I get for my foul body...

Dear Customer
Welcome, and thank you for trusting us
Regarding what you mentioned, the bad odor of the back may occur due to fungal infection of the skin of the back or it may be due to the presence of bacterial infection of the back.

What are the other possible causes ?

Dear customer, the presence of discharge from the lower back, just above the anal opening. This could be due to pilonidal sinus which requires surgical intervention.

What should you do in this case ?

You have to keep the affected area clean and dry and you have to visit your GP doctor as soon as possible so that the doctor could do a full clinical evaluation of your case in order to determine the exact cause of this case then he will treat it accordingly.
  Stay well.   
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Kind Regards

Dear customer 
in case you have any skin disease , you should see a dermatologist so that he can perform a full physical examination
warm regards