I keep falling sick in winter. I feel feverish every two days because of the cold weather, especially after I wake up. I have sinusitis too, so I always have a cold. I feel tired and sleepy too because of this. Sometimes I feel weakness. Do I need to see a doctor who will recommend blood tests? What do I do to build my immunity and weight? I want to be active and not feel tired. My weight is around 48-50 kgs.