I have had DCIS Breast cancer operated in Nov last year and radiotherapy ended mid February this year. I have been doing exercises 2 -3 times a day. Every now and then I forget and lift something, like shopping or moving something and my armpit seems to swell a little and I will have sharp chest pains for a while it takes a good week for it to subside. Is this normal?
You haven't mentioned whether you had a mastectomy or lumpectomy (WLE) or which side breast was affected. I second the 'speak to you BC' but if it's any help, I was diagnosed June 2017, radiotherapy finished October 2017. I was using a rowing machine / forgetting not to lift shopping bags etc and it wasn't until Christmas 2018 that I realised it didn't hurt any more.When I was discharged on my final appointment with my BC I mentioned that it still hurt and she said "it's still early days". Even a lumpectomy seems to be a lot more than a broken bone type thing, which in 6 weeks - often you're back to normal.
I also experienced pains in my chest since radiotherapy I actually think it is heartburn. Seems to happen if I sit in a particular position and I noticed it after going to the cinema and having popcorn. (obviously ok for the last 3 months!) but whether because of the operation we hold ourselves differently as we digest food it causes this issue? I'd never had heartburn before. My radio was over my heart and I couldn't do the breathe technique due to having lost my right elbow in a road accident, so they couldn't position me for the breathe technique and I worried when I first had the chest pains (they went by the morning though) that my heart had been damaged, not had it checked and I've been fine for the last few years 
No harm at all ringing your BC and having a further discussion with her as she may put your mind at ease.
Best wishes,
