Why I always have flu?

You need to start taking a Vitamin D3 supplement every day. Studies have been done on the difference between people taking Vitamin D3 and those not taking it. Those people who were taking 1000 to 2000 IU of Vitamin D3 each day rarely, if ever, caught the flu. You'd probably need to take it for at least a month to 3 months though before seeing a major difference. You should especially take it during the winter months. That is unless your problem is mostly allergies. But Vitamin D3 might even help with that too. I read that it also helps those with asthma.