Update api_usage.py

api_usage.py

@@ -494,7 +494,7 @@ def check_aws_billing(session):
     try:
         ce = session.client('ce')
         now = datetime.now()
-        start_date = now.replace(day=1).strftime('%Y-%m-%d')
+        start_date = now.replace(day=1, month=now.month % 12 - 1).strftime('%Y-%m-%d')
         end_date = (now.replace(day=1, month=now.month % 12 + 1, year=now.year + (now.month // 12)).strftime('%Y-%m-%d'))
         ce_cost = ce.get_cost_and_usage(
             TimePeriod={ 'Start': start_date, 'End': end_date },