Struggling

So before I had cancer I was as fit as a fiddle, an average day would entail an early morning gym session, a full day of helping others at work I worked along side the police in Domestic Abuse, then after work a  HIIT gym classes, I had three children as a single mom and had a healthy work/life balance.
2015 I was diagnosed with breast cancer, I had three surgeries and radiotherapy, I then developed pneumonia, and have struggled to get back to me since. So recently was diagnosed with Chronic Fatigue and have lung issues, been referred to a respiratory consultant as I have had numerous chest infections that has impacted on my breathing. 
The issue that scares me is if I do too much, I literally crash, it feels like I am trying to cope with life through a vat of treacle, I can't even walk a set of stairs without stopping. I don't have the energy to talk even on the phone, I have to sit and watch uncomplicated films, TV shows. It comes over like a huge shroud and nothing except resting for a few days will help. 
The problem is that there is no one I can turn to to get advise, my GP service is so stretched and they seem to just send you away with antidepressants, I am not depressed, I get low yes because I am a quarter of the lady I used to be. But I am not getting any advice as how to manage my symptoms. The real me is a go getting, bubbly, full of fun lady, this is not in my mind this is my body letting me down.
Can anybody advise