First of all, how many samples is "a couple of weeks' worth"? And what is the pH? If your samples are junky, then you might be lucky to get a couple of hundred injections per column.
The sure way to tell is to start with two columns. Run a check sample in column "A" and then put it on the shelf (leave your EDTA buffer in there). Run column "B" for your usual couple of weeks until you can see a noticeable deterioration, then hook up column "A" and re-test it.
If column "A" still looks OK, then the problem is contamination from your samples. If it looks about the same as column "B", then it is, indeed, deteriorating. If your buffer is at pH 8, then you are at or above the operating pH of many bonded-phase columns, and a short lifetime is normal. There are columns that will go above pH 8, and the vendors aren't shy about promoting them, so check with your column vendor of choice for their recommendation.
