can diabetes be wrongly diagnosed when bone marrow found is the smyptons simular

my mother was firstly diagnosed with diabetes.Then was still feeling ill after medication given.With pain in her hips,thighs and generally feeling tired.Was rushed to hospital and sent home. Her gp thought it could be polyimalgia which is arthitis  of the joints.Then after months of tests they still couldn't find the problem .The very last test was a bone marrow test which came back positive.Now l want to know if my mum really had diabetes or was this diagnosis just given because as the smyptons may be simular to those of cancer.Mum has never been right with this medication l thought people could live quite happily with diabetes  is she wrongly diagnosed? I  dont think she has diabetes at all l think it was a mask as they needed to give my mum something and i think this medication she has to have is making her worse.If you never had something in the first place and are given medications aren't there going to be bad side affects to it.