It seems likely that you were prescribed a large-spectral antibiotic in order to treat the lung infection you experienced. Usage of such antibiotics can cause vaginal yeast infections. You can consult a gynecologist to check if that heavy brownish mucus vaginal discharge is due to the infection, or not. A microbiological smear and Pap-test should help you clear up the cause of the mucous discharge..
Bay the way, some antibiotics (ampicillin, Penicillin V, Rifampicin, Tetracyclines) may reduce the oral contraceptives’ effectiveness so additional contraceptive method is recommended while using those antibiotics.