long tearm problems with tiredness, cold and coughing?

So I've had this for about two/three years now and my local doctor can't think of anything it could be. I'm not seeking a definite answer just things to suggest to my doctor.

So I've had low energy for most of my life, that part's not new, what's newer is that any mild exercise comes with major effects afterwards.

The most extreme example was when I was working as a cleaner two years ago: After an eight hour shift plus two mile cycle back home my body would just crash. I'd be too tired to move from my bed for the rest of the day and only half functioning the next day, I'd have a dry cough that would last till the next morning and I'd be freezing cold to the point blankets did nothing and I'd need an external sorce of warmth.

Since then I lost my job due to tiredness, and have fewer days where I push myself to those extremes. However going for a walk will still result in me needing sleep and warmth after, and in winter I can barely go outside without this annoying thing kicking in.

At this point the cough is a consistant thing that's probably just habit more than anything most of the time.

The most annoying thing is the tiredness, I was actually wondering if it was chronic fatigue, but the coldness and cough make me think its less likely.

Does anyone have any suggestions or ideas of what could be causing this?