Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Call emergency services for:
These symptoms are not typical of uncomplicated rickettsialpox and need immediate assessment.
Arrange prompt medical assessment if you develop fever with a new blister-like rash, especially if you also have a dark crusted sore or have noticed mice or unexplained bites in your building.
Early assessment helps distinguish rickettsialpox from other infections.
Seek urgent medical care if you cannot keep fluids down, are passing very little urine, or have signs of significant dehydration such as marked dizziness or unusual sleepiness.
The article also says
Contact a clinician again if symptoms are not improving after treatment begins, the fever returns, or skin lesions become increasingly painful, red, warm, swollen, or filled with pus.
Every sign above is quoted from the sofidex article on Rickettsialpox. If you are not sure, err upward — it is always reasonable to be checked.