My 3yr old has tonsilitis. is it possible my sore throat/pain to swallow after cold gone is this? is it contagious? had it 2.5wks.

Yes, possible: Tonsillitis is usually caused by bacterial infection which is contagious. Depending on which bacteria, some cases are more contagious than others. If you have had symptoms that are not going away after a few days on their own, or you develop fever, swollen glands or rash, you need to be checked yourself. You don't want to keep giving this back and forth to each other for months.