Sore throat when swallowing for 3+ weeks. phlegm stuck in my throat. bumps down the back of my throat. could this be throat cancer?

Phelgm in throat: You are young for throat cancer unless you chewed a lot of betel nuts. More likely you have sinusitis, allergies with phelgm could try Zyrtec (cetirizine) and see if it helps . May be indolent infection/ sinusitis like mycoplasma for whihc you need antibiotics .Since it is 3 weeks would get it checked out by urgent care/ doctor this week.