Do you have an option to talk to an advice nurse at your doctor's office? They could probably steer you in the right direction.
The issue is that a rash at stages is really an open wound. You always need to be careful about what goes on / in your skin. Read the directions of what you plan to use for the sunburn and see if there are any cautions about broken skin.
Some of the home treatments for sunburn are similar to treatments for poison ivy. You might consider using one of those such as taking a bath in an oatmeal or baking soda cool water bath. Calamine lotion for itching. Raw cucumber or potato slices on the rash and burn. If you google for home remedies for treating sunburn you'll see that a number of these do overlap.