Do I have something medically wrong - like nodules!?

Yes, you should definitely see an ear/nose/throat doctor. S/He will probably recommend that you be absolutely SILENT for a few weeks. That means, no singing, no whispering, no talking. Harsh I know, but if you want your voice to heal, it is necessary. After you have healed I suggest you take voice lessons with a qualified teacher so you can learn to sing properly without hurting your voice.