Just finished surgery for perianal abscess. now has lower back pain and tender abdomen. are these inflammation related to abscess?

Could be related: If you have a fever, chills, sweats, feel lightheaded or faint, please see your surgeon or go to an er. Any surgery in an infected area like an abscess could potentially cause the infection to spread (sepsis or blood poisoning) sometimes there can be complications from the surgery itself which could cause your symptoms. Get checked!

Check with surgeon: Other issues may be causing this, i.e. Persistence of a peri-rectal component, or constipation, inflammatory bowel disease, etc. Don't let this answer your question. Confirm with your surgeon.