how many times has patient 61751 been prescribed with polyethylene glycol the previous month?
select count(*) from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 61751 ) and prescriptions.drug = 'polyethylene glycol' and datetime(prescriptions.startdate,'start of month') = datetime(current_time,'start of month','-1 month')