it seems that I just have bad luck with health. I have gotten sick 3 times in 3 months with each sickness lasting for 1-3 weeks. I wonder what I can do about it.

Look into improving your immune system by vitamins but also workings such as a Sun Square. For immediate help practice Yogic Breath by retaining energy, in the same manner of the foundation meditation.

Practice yoga asanas, qi gong or something similar every day.

In addition to the other replies here, this is actually quite common this month. It seems like everyone is getting sick now, so don't think it's just you.

You should do yoga, have a good aura of protection and you should breath Earth element for helping your immune system. Remember to clean yourself with gold energy