Posted: Today at 20:00
So to give a comment that isn't just berating the poster....
For reference I am a Paramedic so obviously not the same quality as a Dr, but I will at least give you some ideas of the things that could possibly be wrong. However I would prefix this by saying that without direct examination I can only give very general advice and would recommend a further visit to the Doctor and if you aren't happy with what has been done ask to see another one.
So breathing problems generally have two sources lungs or heart. GPs have in recent years been very keen to give out inhalers in lieu of a diagnosis of asthma. Often the blue inhaler is given and if there are further problems others are added as a preventative medication to be taken every day.
An asthma attack will usually leave you with a heavy/tight chest you will likely develop a wheeze on breathing out and mucous production will increase. This can be caused by a number of things, cold, hot, pollen, pollution, exercise and a number of stimulating factors. If you get no relief from a blue asthma pump it probably isn't an asthma attack because the drug should open up the narrowed airways.
A similar condition called COPD is usually related to smoking, but could be down to industrial inhalations. So if you have worked in areas with lots of industrial dust or chemicals that might be relevant. It would be unusual at your age.
Chest infections and allergic reactions could also cause some tightness and shortness of breath. There are a few other possibilities but these are some of the most common.
The heart pumps the blood that the lungs oxygenates and so if the heart doesn't work properly the blood cannot oxygenate the organs and body properly, your heart will have to pump faster and you breathing rate will go up. In short you will feel dead tired and out of breath. Again there are a number of reasons why you might get this issue and it does sound like you have had a number of tests to rule these out. I'm not going to go into all the whys and where-fores on this, but I'd say the Dr likely has all these things covered.
The idea about anaemia above is not bad, a simple blood test would give the answer to that and your GP could sort that. Consider the iron levels in your diet and have a look inside your lower lip and eyelids - if they look pale anaemia is a possibility. If you don't get enough red meat or other iron rich foods then again that may be possible. There are other blood conditions that might cause similar but again this is getting to essay length already.
Don't rule out basic stress and lack of fitness, but feeling like an 80 year old suggest your fitness must be very poor. If you are to start exercising do it slowly and again ask for the Dr's advice.
Good luck with it all