Anyone have redness and swelling after mapping?

Hi all, this is my first post but I've been lurking for a while. So first off I want to thank everyone for the great info here. It's been much appreciated.

I started radiation therapy this week on my right breast. They did mapping on Monday and scheduled me to start radiation on Wednesday. By Tuesday I noticed an area on my breast -maybe a little less than 1/4 of my breast - with light redness and minor swelling -kinda like a big hive..rather subtle but noticeable -(I'm about 6 weeks post-op). I expected skin reactions during treatment but I didn't expect this to begin just after mapping. I started the radiation treatments Wednesday and the same area has gotten angrier -not alarmingly but again noticeably. It does not hurt or itch. Basically, I'm just trying to figure out if this is a normal experience. Did anyone else have this kind of reaction start right after mapping? Could that have triggered it? It seems weird to me since radiation hadn't even started. I'm just a little concerned it could be an infection instead of a treatment reaction.

Doctors assistant checked it on Wednesday and basically just said to monitor and call if it got worse quickly. The doctor will take a look at it Monday.