when was the first time patient 7107 was prescribed a medication since 03/2104 via pl route?
select prescriptions.startdate from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 7107 ) and prescriptions.route = 'pl' and strftime('%y-%m',prescriptions.startdate) >= '2104-03' order by prescriptions.startdate asc limit 1