I have a lambda and the trigger for the lambda is an SQS queue. I have not run it at all this month but I am still seeing usage for SQS is this something that is correct behaviour or is there something else using SQS I need to look into.
The AWS Lambda service polls the Amazon SQS queue for any messages that are available. If messages are returned, then the Lambda service invokes the appropriate AWS Lambda function.
Thus, if there is a Lambda function configured to trigger from a queue, then the Lambda service will continue to poll that queue even if there are no messages available. (I presume that is uses Long Polling to reduce the number of calls.)
Thus, you are probably seeing the charges related to the attempts to retrieve messages from the queue.