I need to know what the best treatment for gum pain from wearing retainer?

Needs adjustment. If your retainer is rubbing/pinching your gums, it needs attention from your dental professional. He/she can adjust the plastic to be more comfortable. We recommend patients to try an emory board to slightly sand down the offensive area.
Gum pain. Probably ibuprofen, among over-the-counter medications. You could also try the medications for teething pain in infants like oragel or anbesol.