Welcome to Health Care Magic
It is rather difficult to conclude - as you say.
If the doctor examining and investigating couldn't find, it is less likely from a mail! !?
You should have a second opinion
from a different doctor.
A different set of investigations and some less common conditions may have to be considered.
A Multi Speciality Tertiary Care Centre could help
Life style modifications like diet and exercise - are a must.
A good dietician an help.
Don't get dejected...
There is always hope - it may a question of time and place.
Wishing speedy recovery