Alchemy API is tricky. You're probably reaching the 1000 events a day.
First, you need to understand how the events are count.
Here is an example:
To calculate how many transaction credits a query will cost, multiply historical access and targeting.
Historical Access - each hour of historical access costs 1 transaction credit
Targeting - each query parameter costs 1 transaction credit
Example: Give me news about the company "IBM" from the past 3 days.
Historical access: 3 days = 72 transaction credits
Targeting: 1 query parameter = 1 transaction credit
Query cost: 72 transaction credits
see https://www.alchemyapi.com/alchemydata-news-sales for more explanation
second, you need to check how many credits you've already used. Use this API for that
http://access.alchemyapi.com/calls/info/GetAPIKeyInfo?apikey=YOUR_API_KEY
finally, cache everything you retrieve from AlchemyAPI (bluemix has several options for that)