Truma Ultraflow Filter

Last year I had to have a new water inlet housing fitted to my Lunar caravan. I now use the Truma Ultraflow Filter but have found that it appears to get "clogged up" very quickly. The last one only lasted about 3 weeks before the water pressure started to drop and the pump was struggling to achieve the correct pressure to switch off. A good rinse under the tap gave a brief improvement, but a new filter solved the problem. This is not the first time that I have had this problem and wonder if others have found the same? The filter is too expensive to replace every couple of weeks. Any suggestions?