Itching after mastectomy. Any suggestions?

Most of the time itching can be controlled by topical or oral steroids, cool compresses, or antihistamines after surgery. In more significant cases neurologically active drugs like Neurontin may be used.

So for as far out as
you are from surgery it should not be wound healing itching. Rather it
sounds like the nerves are regaining function and you are having this
electrical sensations as the nerve is able to conduct signals again. There
are some medications that may help you that you will need a prescription for. I
would revisit your breast surgeon and discuss this
issue. Congratulations surviving you battle with breast cancer!

The standard preparations for contact dermatitis will not help you.  Your itching is neurogenic.   I would try Medrol Dose pack and see if it helps.   It may well not but its worth a try.   A drug that almost certainly will work is Neurontin or Gabapentin.  You will need to work with your doctor and see what is the correct dose.   Gabapentin is easily accepted by most people and after the first few days you function fine.  The dose is a little tricky.  I would start with 400 mg 3 x a day and go up or down from there.   Very high % chance this will help you.    It is not a cure but is a great help.    This drug I use frequently on my liposuction patients.