Can I boost my immunity while being pregnant?

I work in a Children's Hospital and I am 5 months pregnant. I am around sick kids all day in my clinic and was wondering how I could possibly boost my immunity so I won't get sick so often. Over the past couple weeks I have had 2 ear infections and now my chest is congested, nose is stuffy, and I am coughing so much that my throat hurts let alone my chest. Is there anything I can take to boost my immunity that doesn't cost a fortune?