Does Multiple Myeloma Cause Bruising?

I have had a severe bout of itching, hives, bruising that started about three days after my last dose of Nitrofurantoin on a ten day regimen, taking it every 12 hours during those ten days. I saw my doctor a couple of days after the reaction started and received a cortisone injection as well as a prescription for prednisone. I am now on my second round of 3-day prednisone medicine, and still having some intense itching, but it is better overall. My question is how long does this type of reaction typically last? I have a lot of bruising where I have scratched repeatedly, but I also have smoldering multiple myeloma, and the bruising could be due to that. Thank you.