Treated for tonsillitis but whole throat/tonsils swollen & red. glands in neck swollen too after 20 days. should it get worse to get better?

Culture: If the tonsils are red and swollen for 20 days and an antibiotic has been unsuccessful I would strongly recommend a culture of the throat to rule out a viral infection or a specific bacterial infection. Finally, infectious mono needs to be ruled out. No it should not get worse before it gets better. You need a specific diagnosis. See an ENT doctor.