Pain in good breast??

I wonder if anyone else has the same but I’m on my second dose of chemo now and since I started I get a dull pain in my affected breast, which is good in my opinion, because it’s telling me the chemo is doing its’ job, but I also get a similar pain in the other one. Has anyone else experienced this? Is it a hormone thing? I’ve had the good breast scanned and was told it was clear, but sometimes I just worry and wonder!
Ginnyx