My Entire Left Arm Has A Moderately Heavy Weakness To

My entire left arm has a moderately heavy weakness to it which began a week ago. It started with a body ache type intermittent pain in my left thigh but that left after one day, and now it has been the moderately heavy feel to my forearm and upper arm, which did extend to my upper left shoulder into my neck. I was diagnosed with left breast cancer where they took 6 lymph nodes in January 2016. I saw my oncologist NP and she did not think it related to my breast cancer. I work with a lymphedema nurse and she confirmed that I don't have lymphedema but that it is most likely a muscle issue. What happens is that when I hold a filled beverage glass for example, I will need to put the glass down soon because it is getting too heavy. A gallon of milk really gets heavy fast. For medical hx purposes, I've had ulcerative colitis for approximately 20 years, autoimmune chronic hepatitis which showed itself in June this year that apparently has been dormant all this time, and diabetes. I had bilateral mastectomies in January 2016 with breast reconstruction in September. I will see my pcp next Wednesday, Dec. 14, 2016 and have been very puzzled for a week now. Is there anything you can think of that I should have my pcp check out? Thank you.