TannieT With the discomfort you're feeling it would be useful to speak to a medical person to understand what's going on and how to make it better.
If you're not keen on speaking to the surgeon, do you have a breast care nurse that you could contact to get their thoughts on what might be going on? Mine connected me to a lymphoedema therapist who I saw recently and talked about the various sensations (and lack of!) I've got going on in my arm and armpit. She showed me specific massage techniques to use which seem to be helping.
A possibility aside from the healing process could be cording. Although cording happens more with lymph node removal, it can happen after mastectomy as well. Here's some information from BCNA about cording.
I hope that you're able to get some help and relief from those pains.