Painful Peripheral Neuropathy

The goal of this clinical trial is to determine whether quantitative sensory testing (QST) can be used to classify participants into pain sub-groups and predict who will respond best to certain pain treatments in participants with painful peripheral neuropathy. The analgesic effect is evaluated by measuring pain intensity and Patient Global Impression of Change (PGIC). This study is a 3-period cross-over trial. This means researchers will compare 3 different drugs (pregabalin, duloxetine, and placebo) over a period of 19 weeks. Participants will: * Undergo a quantitative sensory testing (QST) exam. * Provide a blood sample. * Complete questionnaires on the computer. * Take the study drug as instructed.