Why would tonsillitis keep coming back?

I had tonsillitis last week with the usual symptom of fatigue bad head the usual anyway for a few days the symptoms went so i presumed i was better. Anyway it has come back worse my throat is red raw with white spots yuck my throat feels like i have swallowed a cactus i cant eat much. I am losing weight. I am run down i gave birth 11 weeks ago. I am not sure why i keep getting every infection illness going anybody have any ideas how to perk up my immune system as it is a nightmare to get into see my doctor.