Immune and worsening to Amoxicillin

i am 19 years old and i have lost count of how many times i have been put on Amoxicillin even as a young child (who was always sick) i was put on 500 mg 3x's a day for 20 days in October 2008 for a bad sinus infection. i wound up in the hospital in December 2008 for an emergency procedure (pilonidial cyst) and was put on keflex for the infection in my body. it's the end of January 2009 and i am back on 500 mg 2x's a day for a sinus infection. it hasn't worked at all, i'm pretty sure that i became immune to it and i cannot take anything w. penicillin or sulfur. as the pill doesn't do anything this time i have developed a horrible cough which worsens at night and i find myself choking cause of no air and i cough up WATER yes, WATER or a water/slimy liquids and i feel it come from deep in my chest (post nasal drip?) what can i take? i'm pretty sure im developing a respiratory infection or walking pneumonia.