need to change my med.'s a little. Do not want to go up, but presently what I take is not working w

I have been living with chronic pain for 30 yrs.  I am presently taking Kadian 80 mg twice a day (extended release Morphine) and 4 30 mg Oxycodone for breakthrough.  I recently had knee replacement surgery, for which dr. added, morphine 30 mg, IR.  now I am just taking my regular chronic pain med.'s which have not been working that good for some time now.  I want to know what I can take that is similar to my regular treatment, but will work better?  what is diff. between morphine IR 30 mg. ad oxycodone IR 30 mg.  Also, since I stopped the added 30 mg IR morphine for acute pain, I have been sick.  My stomach hurts, I can't eat, am I having withdrawal symptoms from the morphine 30 mg. IR which I took post surgery 1 month since surgery, but ended IR morphine a week ago.  Any suggestions?