Rob1 I'm not surprised that you're upset at the swelling - it sounds uncomfortable and unexpected. It's good that you've been getting it checked out.
I don't remember what was said about heat - best check that with your BCN just in case.
Recently I saw a lymphoedema therapist who provided instructions for massage to hopefully avoid having lymphoedema in the future. Do you know if your healthcare team has someone like that available? They may be able to help.
I hope that your GP takes a good look and can tell you the cause of the swelling. Hopefully they can provide solutions for you.
12 days is not a long time. Recovery will take time and every body is different but hopefully you're reaching the peak of the discomfort now and will start to see improvements little by little.