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I am sorry you have noticed this change in Boagie. From what you describe I am concerned that he may be anaemic or possibly have a condition whereby the blood isn't being pumped around the body properly (heart disease). Both conditions cause a reduction in the amount of oxygen reaching the muscles, skin and limbs. This will show as lethargy and pale colouration to the gums.
I would strongly recommend you take Boagie to your vet for a full physical examination and potential blood test to highlight any abnormalities in red blood cell number. Often conditions such as anaemia or heart disease develop slowly so the body can adapt and therefore the dog doesn't appear to be suddenly unwell, it is something they can compensate for initially, but then often all of a sudden they become very ill, very quickly.
Good luck and I hope there isn't anything too serious going on.
I also forgot to say that the initial examination and blood testing for anaemia is very simple and straight forward without the need for complex investigations initially.
This definitely highlights the need for a veterinary examination. Blood values can change in hours/days so it is distinctly possible that things have changed within 12 months. Vaccinations will have no bearing on his current clinical signs. It certainly sounds as though he is in discomfort and distress and as such should receive veterinary attention.