what's up with my immune system??

This is the basic question I'm asking myself now, and for the past month.
After getting better from my 8-month-long sinus infection, I felt really optimistic. No surgery! I can breathe! I'm not congested!
Then, a month later, I got a cold, with my typical symptoms of sinus congestion.
A week after that, I got some sort of stomach bug or parasite.
About a week and a half later, I felt like I was getting another cold, and then it turned into a recurrence of a virus I got three years ago when I first moved to Bogotá.

Last night I slept for 12 hours, and right now the thing I most want to do is go take a nap.


I've started taking Scott's emulsion again, which I think helped my immune system health while I was taking a spoonful daily (I ran out about a month ago).
But really?! What's all this about?!

Another theory is that my mild case of chicken pox (varicela zoster) as a child may have left me susceptible to catching and retaining other viruses in the same family (the gingivostomatitis that I got three years ago, and that is now acting up again is in the same family of viruses). Are any medical professionals reading this? Does that even sound possible?

Or, any tips on boosting my immune system health? I'm sick of being sick.