Contralateral BC worry 11 years later

Hi Ladies, I return to this forum eleven years after diagnosis of BC at age 33.  I had triple negative, stage 1, grade 3, lumpectomy, AC and radiation. Over the years, many tiny scares have hardened me up a bit and I certainly don't live in fear anymore, but with a recent concern I am finding myself a bit lost, so I thought I would just put these feelings out there in the universe and see what returned to me.  My contralateral breast is very heavy and swollen.  It's not hot, no rash, just tender and sore and I can't really feel through to any obvious lump.  My period is on it's way, but I have had tender breasts from PMS before and this is nothing like it. Any thoughts, ladies?  Yes, I have made an apt with family doc for next week.  I can't think of any injury to my breast, and I don't think it's mastitis because I have had infections before and I was in more pain than this.  Another strange thing is my right arm down by elbow is a bit sore, in exactly the same way my left elbow hurts all the time from very mild lymphedema.

Thanks for "listening"

DuckieGirl