Could it be from the right muscle since I’m right handed?

Thank you for sharing your question. These symptoms require a more in-person examination of your tissues to try and provide information. I would follow up with your surgeon for the best advice.

Dear sheannnaa,
I understand your concern. However, without a proper assessment, it would be difficult to determine what went wrong. It is best that you visit your plastic surgeon for further assessment or ask for a second opinion. Only after a thorough examination, you can get proper recommendations and advice.
Daniel Barrett, MD
Certified, American Board of Plastic Surgery
Member, American Society of Plastic Surgery
Member, American Society of Aesthetic Plastic Surgery

You might consider having the lump removed in case the scar tissue is causing some pain and also to be checked. the warmness could be from small sensory nerves that are around scar tissue. I doubt the weakness of your arm and shoulder are from your breast. You might want to ask your medical doctor to X-ray your neck to be sure you do don't have and neck issues.

The symptoms that are concerning you are best addressed after an in person examination. Sometimes nerves can get trapped in scar tissue, causing discomfort, but it's not possible from your description to say exactly what is causing your issues. I encourage you to continue to follow up with your surgeon.