One: if you have herpes your ex does not necessarily have it too and someone can have the virus for a very long time and not know it.
Two: the HPV blood tests are specific. It's not a test that is done routinely so unless thats what your blood was being drawn for it could very well have gone undetected.
Three: there is actually much contraversy about HPV blood testing. It spots antibodies after exposure. The problem with it is not so much that it is unreliable as it is difficult for clinicians to read and therefor is often misread. Hence, unreliable.
Four: if you are getting sores every few months why wouldnt you question what the source is and have it checked. Sores are a BIG sign of herpes.