I want to sing but I almost always have a sore throat!?

I really like to sing but I have a huge problem. I wake up every morning with a sore throat that makes my voice hoarse and it takes a long time for it to go away. And on top of that, I don't have much of an immune system so every time it's a bit chilly outside I immediately start coughing. Does anyone know any long-term remedies for this?