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 now if you or someone else may have an infection and has any of the following:
For a baby or young child, emergency signs also include being floppy or unresponsive, struggling to breathe, having a weak or unusual cry, or being difficult to wake.
Seek urgent same-day medical assessment for an infection with worsening symptoms, repeated vomiting, much less urine, increasing sleepiness, severe pain, or fever and chills in someone at high risk of serious infection.
Do not wait for every typical symptom or for a rash to appear.
If these changes occur while you are already in a hospital or care facility, alert staff immediately.
Sudden deterioration should be treated as urgent rather than saved for a routine appointment.
The article also says
After discharge, contact your usual healthcare service for non-emergency problems such as ongoing fatigue, reduced mobility, sleep disturbance, low mood, or difficulty managing daily tasks.
Every sign above is quoted from the sofidex article on Sepsis. If you are not sure, err upward — it is always reasonable to be checked.