Although a small amount of spotting between periods can be normal, especially around the time when ovulations occurs, you are right that continuous spotting for an entire month is never normal.
Probably the most common cause of continuous spotting like this is a side effect of various birth control
methods (including both pills, IUDS, and other methods). Because these methods exert hormonal effects on the lining of the uterus, they can sometimes cause this lining to become friable and full of blood vessels, which can lead to spotting.
Another common cause of spotting is a sexually transmitted infection, such as chlamydia or gonorrhea, which causes inflammation of the cervix and uterus. Often, but not always, this is accompanied by vaginal discharge or burning with urination.
If the spotting is worse after you have sex, then this is most likely to be a problem with the cervix, which could include an infection, a polyp, or a sore. This would definitely need to be checked out, as sores can turn out to be a risk for cervical cancer.
Finally, in older, post - menopausal women, spotting is worrisome because it requires ruling out endometrial cancer.
With all of these possibilities, the first step would be to schedule a visit with your OBGYN doctor
in order to have a good physical examination.