I have had a red and tender penis for over a year now. started while in a relationship with an ex-girlfriend. before going out with my current wife a month after my break up, i had a full sti panel (except for herpes). my gp examined me and found no signs

For sure no STD: Since you have been professionally examined and no abnormality was found, I have to believe that nothing is wrong -- i.e. that your impression that your penis is "red and tender" is mistaken. Maybe it's primarily psychological. But if you are convinced there is definitely redness and tenderness, get a second opinion from a dermagolotist. In any case, no STD causes such symptoms. Good luck!