For some men and women, it's noticeable when they have chlamydia, but as the symptoms can just cause discomfort, some people walk around for years not knowing they are carrying the infection. More than half the men and women who have the infection are unaware. This lack of awareness makes the infection all the more easy to spread, especially if you have a lot of sexual partners.
It's a sexually transmitted disease (STD) that has to be treated with antibiotics. Whilst you may not have any discernable symptoms, it is possible that may get symptoms like lower abdominal pain, bleeding after sex or between periods, pain during sex or when you pass water, or an unusual vaginal discharge. You may have not had these symptoms and have only realised you were carrying it because a partner had a positive test, but the impact on your ability to conceive can be very serious.
Chlamydia, like some other STDs, can quite easily block your fallopian tubes which prevents your egg passing down for fertilsation.
(In some cases, an infection or scar tissue from a previous illness or treatment can cause a blockage in the fallopian tube and an ectopic pregnancy ensues. This is painful and dangerous for the woman and the pregnancy is not successful.)
If you have had chlamydia more than once, it is of special concern. If you know you have had a problem with the infection before or think you might possibly now, mention it to your doctor who can have a test done and remedy the situation for you. It is important than any partner you have is also treated as the infection otherwise will reoccur.
Note too, that the infection can affect your baby's health even if it does not affect your conception. (It can cause miscarriage or premature birth, and at birth it can be passed to the baby and bring about pneumonia or a serious eye infection.) Unfortunately it is not one of the routine pregnancy tests and is not picked up in blood or smear tests, but do raise it as a concern if you fear you might have it. It can be treated safely when you are pregnant.
You can find out more about chlamydia, its symptoms and treatment at the Family Planning Association website.