Chlamydia is very easy to treat with a simple course of antibiotics, however, if left untreated, chlamydia can impact the entire male reproductive system. The bacteria which causes chlamydia (chlamydia trachomatis) may cause inflammation of the urethra, testicles and prostate gland. This inflammation may lead to issues in both the quality and mobility of sperm, so male fertility could be compromised.
Untreated chlamydia may also lead to a condition called epididymitis, a condition which means the tube which holds the testicles in place (the epididymis) becomes inflamed, this may make urination and sexual intercourse painful. Infection, associated with epididymitis may also lead to fever, headache and pain in the abdomen.
As mentioned, chlamydia is very easy to treat if caught early, so make sure that you are regularly attending STD testing.