Losing large amounts of weight often causes the issues you are describing. I'm not a coach, but since you didn't mention it, why don't you try adding in weight training? Losing weight often equals losing muscle mass and when we get older (I'm a couple of years ahead of you), we need to concentrate on building muscle mass to counteract the natural process of aging. If I was in your position, I would get some professional advice: strength training/exercise physiologist/PT (make sure it's a real professional) and a registered dietician.
I think that a lot of people (women) ignore the strength issues, which can cause a lot of problems as we age.