Arnica for hematoma?

I got my MRI results today which showed nothing new really (yay!), just a fairly large hematoma from the stereotactic biopsy. The surgeon says he'll need to cut out the entire hematoma to be sure he's getting the DCIS. I have read that arnica cream can be helpful in resolving hematomas.... is this something that can be bought at any drug store/walmart, etc.? Is there anything else I can do to help it along? I want to get it as small as possible prior to lumpectomy (if indeed I decide to have a lumpectomy--still have to make that decision, uggh).

MRI also showed a slightly enlarged lymph node but they said it did not have any unusual characteristics. I'm hoping it's just a result of the biopsy. Has anyone ever had this happen? That bought me an automatic SNB. 

Thanks, ladies!

Andrea