Talk to your colleagues – they may have a similar problem.
Talk to your supervisor about the extra work and request additional time on your SWF or a reduction of your workload. If your supervisor does not agree, log your workload (such as marking and meetings) for the semester.
Write down how much time you actually spend marking, performing committee work, and so on.
Later in the same semester or the following semester, you will have actual figures with which to argue your case before your supervisor and possibly before the Workload Monitoring Group.