Heel spurs occur as a result of a period of increased traction having occurred. This is often the result of having been overweight (currently or historically), but can also just be the result of repetitive 'overload'.
Heel spurs are better positioned as a description than a diagnosis. The reason that a heel spur being given as a diagnosis is unhelpful is because:
Heel spurs are lumps of bone that have grown as a way of the body responding to the extra traction going through the bone the structure joins to. Although pain fluctuates, the heel spur's size and position does not fluctuate... so if you have pain in one part of the heel and then a different part or you have a day without pain, that does not mean that the heel spur has gone.
Also, so many people have heel spurs and have no pain at all... so take it from me, you don't need to worry about that heel spur you were diagnosed with!
Heel spurs are a description of a radiological (x-ray/imaging) finding. Although they can often look very dramatic and painful, they are very rarely the cause of your pain.