RDS cost jump starting in April, but there doesn't appear to be a database

Hello, starting in April our RDS costs jumped from $225 to $506 per month and have stayed that way since. Nothing changed on our hosted app and we didn't have an influx of new users. Our other costs remained relatively constant.

I am new to this whole thing here, and don't really know where to look to see why our costs jumped so much. I checked out the RDS management pages, and found that we have 2 databases, production and staging. Over the last week we have not had more than 3 connections simultaneously on the prod DB. CPU says 5.45% which doesn't seem like much.