Difficulty jumps up and down dynamically but this should not be problem, it is to be expected from retarget each block, also right now there still large swings in net hashrate.
You can mine on PPLNS pool (such as digiforce.cc) which will smoothen rewards for you.
About reject rate, can you provide more data? I am both mining and administrating pool and i did not notice increase in rejects.

hey digibyte.  been mining at coinium and since the new diff took place the diff has been all over the place.  never consistant.  it will go from 8 to 9 then jump to 12 to 15 then back now to 7.  cna you explain as to why it does this.  and im getting much more rejects with this new diff change.  plz explain.