Sounds like a fungal infection, like yeast or jock itch. It might also be eczema or dermatitis. Have you been do a doctor?
Since it's been going on for so long, you may need a prescription strength medication, and different fungal infections respond better to different meds, and eczema will need a different med than a fungal infection, so don't try to home treat without seeing a doc. Any urgent care doc should be able to help if you can't get checked by your regular doctor. Don't put it off any longer.