Yes, cystitis can be due to STD. Bacterial cystitis is an inflammation of the bladder, caused by bacteria entering the bladder via the urethra. Bacteria are the most common cause of cystitis, and may be introduced into the urinary system for many reasons. Infections such as chlamydia and gonorrhoea can cause symptoms similar to cystitis, particularly when they are present in young, sexually active men. You are on the right antibiotics. Plesae continue on the same.