Yes the clutch fluid loss is causing this. I had this happen a while back on my CD5 (F22B1 though) and eventually I just drove it without using the clutch at all until I was able to get it fixed. The clutch fluid is what enables it to open up when you push the pedal down. With less fluid than necessary there is not enough pressure to engage the clutch all the way - hence the difficulty in engaging gears and also the shuddering.
Definitely find out where it is leaking and get it fixed - likely a hose or clamp but could also be one of the cylinders.