how much azithromycin dose has been prescribed to patient 50065 since 04/2104?
select sum(prescriptions.dose_val_rx) from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 50065 ) and prescriptions.drug = 'azithromycin' and strftime('%y-%m',prescriptions.startdate) >= '2104-04'