Thanks for asking the query,
Difficulty in mouth opening can be due to fracture
of the mandible, as you mentioned you had a punch there are chances of condylar fracture.
Due to swelling in the region there can be trismus
causing difficulty in mouth opening.
Visit to an Oral and Maxillofacial Surgeon and get the check up done, see for occlusion, mouth opening, mobility, sweling, mobile segment or fracture line.
Take an OPG x-ray to confirm the diagnosis.
Start with the course of tab Amoxiclav
625 mg and tab brufen
TDS for 3-5 days.
mouthwash gargles twice to prevent infection.
Hope this helps out.