Ola,
I'm NHS admin, you need a work load review, and a proper one at that! I supervise a medical secretary and the role we have her doing is a new role and since I'm the only one that knows the service I've ended up supervising. I have gradually introduced the work to her a bit at a time (she works for three services providing a days cover for two services and and then spending three days a week working for her main consultant). I have my own concerns about the workload so since we've started getting her doing more and more of her role I have been meeting with her weekly to check up how it's going, review the emails she's getting to make sure she's not being dumped on and generally making sure she's doing ok. As far as I'm concerned a problem with her workload would either be a training issue or it's too much, so far she's doing brilliantly but I suspect it will get too much eventually as her main service is very complex. Your manager/supervisor should be keeping an eye on you in the same manner if you raise concerns about your workload.
I get on very well with my manager and she knows that I'm more than happy to let the sh!t and the fan meet if I feel I have a point to prove in terms of workloads not being recognised. Unfortunately in the NHS this occaisionaly has to happen before the powers that be take note which really irritates me, it seems like things have to get to crisis point sometimes before people understand what you've been trying to tell them. The department I'm in now I am quite lucky as they do listen, and they've learnt that when I say there's a problems, there's usually a big bloody problem but the previous deparment, my god, the management were a bunch of morons! Hence why I left them ;o)
Have you thought properly through about what is actually causing you the issues? As in is it the letters turn around time? A phone that doesn't stop ringing? Constant fire fighting, and is so, what's causing this surge of problems? And also, what you think can be done to solve some of the problems. You know how it works, go in there with a list of issues and some suggestions of how they might be fixed rather than just a list of issues. Document your meeting and what is said, if your manager has any sense they'll do it anyway, (I do so that if my secs workload proves too much, I can demonstrate it's been regularly monitored and revised).