Feeling sick all the time

Hello all, I am wondering if I can get some help. I am a Canadian living in Mexico (playa del carmen) 

I am 47 years old and am very healthy and active. I never got sick all that much growing up but in my 40s that seems to have changed. Also since moving to Mexico a year ago I have been battling one thing after another.

Most recently got a parasitic infection. (3rd this year)

I feel like my immune system is weak. Every time I go to a doctor here all they do is give me antibiotics. 

I have been taking probiotics, Oregano oil among other things and nothing seems to work. Any advice?

Richard