Acute sinusitis is usually caused by a virus and typically improves within two to three weeks without antibiotics. Thick or coloured nasal mucus alone does not mean you have a bacterial infection.
Helpful measures include saline nasal rinses, decongestants for a short time, pain relief, and rest. Antibiotics are generally only considered when symptoms are severe, last beyond about ten days without improvement, or get better and then suddenly worsen, which can suggest a bacterial infection.
See a doctor promptly for severe headache, swelling or redness around the eyes, vision changes, confusion, or a high fever, as these can indicate complications needing urgent treatment.