Repeated infection is an indication of lowered immunity. You being 20 years old, there is less chance of decreased immunity unless you have these problems mentioned below:
1. congenital immunodeficiency
2. On drugs like strong antibiotics, antimalarials, steroids
In your case, I feel use of many antibiotics could be the cause of your immunodeficiency.
Crohn's disease is also associated with an immunodeficent state.
I still advise you to get screened for Crohn's and other immunodeficient states.
Your doctor will help with this and prescribe necessary lab tests.