Post radiation

Thanks for your replies. There's no pain, heat or redness coming from the breast so I don't think there is an infection. It could be breast lymphoedema though I didn't get lymphoedema in my arm after my lymph nodes were removed. I'll give the hospital a call and see what they say

@Yango as the others have said definitely get it checked out for fluid or infection.  However my breast did swell during and after radiation.  It stayed larger for many many months before gradually reducing. It is still slightly larger than before treatment 18 months later. Not that anyone else would notice but I can tell. However it's not sore or painful in any way so if you are experiencing pain please get it checked out.

Definitely get it checked out. 
I finished radiation 4 months ago (30 rounds) and my breast was a tad smaller than the other with a dent, where the tumour was removed.  It now looks about the same size as the non radiated breast and the dent is not visible any more. 
My radiated breast was a lot harder than the other one and the pain was intense especially the nipple.
I did get it checked out by BC nurse, GP, Surgeon and oncololgist - anyone I visited as I was really worried about it, they all said normal. 
The good news is the pain is gradually getting less.  I guess everyone's body reacts in different ways.
Good luck and I hope everything settles down soon. xx

Yep - as @lrb_03 has said - definitely check with your breast care nurse if you have access to one & try & see your GP (or another Dr in the practise if yours is not available) today as many of the specialists/surgeons will be on their Xmas break until mid January - tho some will be 'on call' at hospitals.  When my husband or I have something urgent, I just go to the GPs office & say I am prepared to sit & wait until I can see someone ....

Is it hotter than normal? Is it painful?  The heat from the radiation should have dissipated by now - if it IS hot, it could be a sign of infection.  It could also be a seroma (fluid) that may need draining - but an ultrasound may be requested to check on that.

All the best & I hope you can be seen sooner than later xxx

The breast can swell as a result of radiotherapy, I think. Do you have a breast care nurse you could discuss this with?
I have ended up with breast lymphoedema, for which I see a lymphoedema therapist, and a masseuse that specialises in lymphatic massage for lymphoedema.  I'm not suggesting that you have lymphoedema but a visit to a lymphoedema therapist may be worthwhile. If you don't know of one in your area, follow this link 
https://www.lymphoedema.org.au/the-register/find-a-practitioner/
Type in your postcode to find your closest therapist 
Also, is your breast showing any signs of infection? Maybe see your GP to get that side of things checked out, too.
The shrinking of the breast, if it happens, happens slowly over time. It doesn't happen to everyone, in fact, I don't know what the frequency would be but I'd imagine it would be a minority.
Take care