Welcome to HealthcareMagic forum.
Pain and swelling due to DPT vaccination
usually do not continue beyond a week or two and gradually decrease after the first two days .
In any case if it's worsening then there are chances of it being infected or developing an abscess
I would recommend you consult a pediatrician
or a pediatric surgeon as soon as feasible to examine the swelling , rule out infection / abscess and start appropriate antibiotics .
Sometimes an ultrasound of the part may be required to confirm the diagnosis .
Hope I have answered your query.
Wishing your child good health.