Struggling with Radiotherapy side effects. Can anyone help?

I have 2 different cancers, breast and lung.

I had 20 sessions of radiotherapy for lung, 8 weeks ago, and I am still extremely breathless. Had a course of antibiotics which did lesson the phlegm, but I am still laying down after about 4 hrs out of bed.

I am 74 yrs old, but usually fit and active. 

Any advice would be much appreciated.