imatinib side effects

I don't have CML but I am told it is rare but similar to it. I have been diagnosed with a condition called myeloproliferative neoplasm with a PDGRFRB rearrangement. My condition responds very well to imatinib. I have been on it for a little over three years now and my blood counts look good. I did well on the drug at first but for about the past six months I have been experiencing some adverse side effects from it. I have muscle aches and joint pain as well as some digestive issues. The worst part is the fatigue I have from it. I feel tired most of the time and if I try to do anything strenuous it really wipes me out to the point that I actually get short of breath. I haven't been able to work for the last six months and it hasn't given any indication of easing in severity. Has anyone else experienced this level of effects from the drug? I talked to my doctor about lowering the dosage but he said that it might run the risk of my disease becoming resistant to the drug. The bottom line is the best option for me is to stay on the 400 mg a day to keep my disease in remission. Has anyone else been experiencing the same type of symptoms? Thanks in advance for any replies.