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 difficulty breathing, swelling of the tongue or throat, collapse, confusion, or other severe symptoms.
Contact the treating service promptly if the affected area continues to expand, pain is increasing, fever persists, new pus develops, or there is no improvement within two to three days of starting antibiotics.
A clinician may need to reconsider the diagnosis, look for an abscess, or adjust treatment.
Seek urgent advice if vomiting prevents you from taking antibiotics or if you develop hives, facial swelling, or other symptoms of a medication reaction.
To reduce the chance of recurrence, care for cuts promptly, keep skin moisturized, treat athlete’s foot, avoid walking barefoot where injuries are likely, and inspect the feet regularly if you have reduced sensation.
Work with a healthcare professional to manage chronic swelling, ulcers, eczema, diabetes, or circulation problems.
Routine follow-up may not be necessary when a mild infection is clearly improving, but some people need reassessment because of the infection’s location, severity, or underlying health conditions.
The article also says
Follow the review plan given by the treating clinician.
After recovery, skin discoloration or mild swelling may remain for a while.
This does not always mean the infection is still active.
Ask for review if the area starts becoming hotter, more painful, or larger again.
Every sign above is quoted from the sofidex article on Cellulitis. If you are not sure, err upward — it is always reasonable to be checked.