Swollen and painful breast

I finished my Radiotherapy in early Feb and have currently been home in the UK for a visit since the beginning of March. During this time I have also met up with my Husband in the USA. He was on  a training course with his job and the two us had a wonderful week to ourselves.  I'm back in the UK now and fly back to Perth tomorrow.  Throughout the trip both my breasts have felt extremely sensitive.  At first I thought it was my hormones returning back to normal as I had cramp and it felt like I was going to take a period. My periods stopped completely after chemo. However on the flight yesterday from the US to the Uk the breast where I had the lumpectomy began to feel quite firm. I don't know if this is because of the 7hr flight or whether cabin air pressure can even have any impact on such thing.  My right breast feels completely normal but the left feels quite firm and really warm. I will definitely get it checked on Monday when I'm back but I feel physically sick.  Sometimes I wonder if it's all in my head and I'm  being extremely paranoid but asked my Mum to check with me and she felt the same.