Thanks for writing in.
Your pain and itching in the perineum
region is not related to your L4 L5 disc problem. It could be that you are having a local infection in the area. A simple course of antibiotics or antifungals (tablets or ointment) may solve your problem (to be taken under medical supervision).
It is quite possible that due to localised infection, you are experiencing discomfort in erection.
hope this helps.