Hi sal
Sounds as though you having an adsorbtion problem with the infusions sets, and will need to change your site sooner than you did or perhaps change the type of infusions sets you've been using (not sure what ones etc fit the medtronic pump, but your DN will be able to let you know)
With my pump I fill the cartridge up, then change my infusion sets every 2-3 days, and the cartridge when needed... Again not sure what infusion sets for the medtronic, but I use rouche tender-links, which do come in two sets one set includes all the canular and tubing, the other is just the canular, so for me it's a case of changing the whole lot, then the next site change I just change the canular, does cut out some of the mucking around involved...
Hope this helps