Hi. I'm so sorry to hear about your Nephews troubles. Let me see if I can give you some basic information that will help you figure out what needs to be done in his case.
I'm going to start with the Low
Haemoglobin first. Anemia is a big issue which lots of people suffer from all over the world. I don not know the cause of your nephews anemia, but the disease has been known to weaken the immune system and make people more susceptible to allergies and infections in general.
Now, the
dry cough, stuffiness,
dizziness and headaches all make me think that he has a problem in his Upper airway. A
Sinus infection or
Ear infection comes to mind (your
inner ear is connected to your airway, hence i included it). But that wouldn't explain why it happens in the dry and cold seasons.
So another logical explanation is that your nephew has a type of
Reactive Airway Disease. This is the bodies immune system becoming hyperactive and causing inflammation in the airway in response to harmless stimuli (like cold, dry air). The inflammation from the Reactive Airway could explain all of his symptoms pretty neatly and also explain why this problem is recurrent and seasonal. The treatment is to take inhaled medications to calm the airway down and any good Primary doctor can put you on the right track as to what is available in your area.
One neat trick that works with some of my patients is to sleep with a humidifier in the room. It makes the atmosphere less dry and irritating to the airway. I can't guarantee it will help here, but it's a harmless way to help and it works more often than you'd suspect. If the humidifier doesn't work after 10-15 days of trying it out, then you can always take him to the doctor for more active treatment.
I hope this helps. I really hope your Nephew is doing better. Feel free to contact me through HealthCareMagic.com for more on this or any other health issue.