Loss of suction on medela

I have a Medela pump in style advance that occasionally use. For the past few month I have noticed that the suction isn't how it use to be. I can't get anything out. If I do (which is rare) its mostly foremilk. Has anyone had this issue before? What did u do?
 I've only had it since January and use to pump once a day until maybe 3 months ago. I have already changed the membranes. Another thing is that I've noticed that milk has been getting into the tubing and have to constantly clean them. Pretty much after every pumping session.