As I entered my thirties, I began to have two days or so of brown spotting before my period. I know this does not affect my fertility, because I've had a child since then, even with the spotting.
But there were also several times in the past decade that I began having this spotting, as you say, up to a week before my actual period began.
And each of these times, it turned out I had polyps- I've had a polyp removed twice now from my cervix and twice from my uterus. I seem to be quite prone to them.
These polyps are nearly always benign- mine always have been, and I've read that they can contain malignant cells in less than 1% of cases- but doctors like to remove them anyway, just to be sure, and also for relief of symptoms such as spotting and sometimes bleeding between periods or after sex.
Having a cervical polyp removed is simple; they do it in the office, without anesthesia. Since the polyps are usually tiny and hang by a thin stalk, they simply pull it off with tweezers, then send it to a lab to make sure it's benign. I personally could not even feel this. The polyp itself has no nerve endings. It is simply an overgrowth of tissue.
Having a uterine polyp removed is more difficult. It requires day surgery (a d&c) and anesthesia. They scrape out the lining of the uterus, and the polyps along with it. But it's still not too terrible. No real pain afterward, and back to work the next day.
I only mention this because both cervical and uterine polyps are common; apparently about 20% of women get at least one. They are most common in women past thirty, who have given birth multiple times. In rare cases, they can impede conception- a cervical polyp can grow large enough to partially block the opening of the cervix, not allowing sperm through, and a uterine polyp can act as a natural IUD, preventing a fertilized egg from implanting. So of you are trying to conceive, it is best to get checked for polyps and have them removed, if they are present, as they could be hindering your efforts.
The most common- and often the only- symptom of them is spotting for several days before your period.
This information may or may not be helpful or applicable in your case, but it's what I've learned in my six or seven years of dealing with polyps, so I like to put it out there, when I hear of other women dealing with these symptoms.
Above all, remember that if you have one, it's not a big deal. More of a nuisance problem than anything else. They are almost never malignant, and are easily removed (although do tend to recur in some women).
Apparently they are caused by estrogen, so after menopause, they are very uncommon.