Hello and welcome to Just Answer. This may be due to immune suppression just from being so ill. It may also be a drug reaction from one of the medications that you are on. Can you list the medications that you are on?
Some medications that can cause this are nonsteroidal antiinflammatories, beta blockers, and medications for angina.
Over the counter products that are good- Gum Rincinol mouth rinse, Colgate Peroxyl mouth rinse, Chloraseptic throat spray for numbing.
You will find the most relief if you can rinse 5-6 times daily.