Along with the advice about diet and a physical, you might consider taking a multi-vitamin and talk to your doctor about your energy/motivation when you get your physical.
I used to be puzzled as to why people would take vitamins in general, thinking that if you need vitamins, you should adjust your diet. I still think that more or less, but started taking vitamin B when I had some nerve issues and noticed my energy, mood and motivation was for sustained periods of time better than it had been probably since I hit puberty. I later went to the naturopath for other health issues and blood work showed I was borderline hypothyroid and had very low vitamin D levels. I have been taking supplements for both of those (stopped taking vitamin B awhile back because it started affecting my sleep for some reason) and they have also helped with my mood and motivation.
I used to be puzzled as to why people would take vitamins in general, thinking that if you need vitamins, you should adjust your diet. I still think that more or less, but started taking vitamin B when I had some nerve issues and noticed my energy, mood and motivation was for sustained periods of time better than it had been probably since I hit puberty. I later went to the naturopath for other health issues and blood work showed I was borderline hypothyroid and had very low vitamin D levels. I have been taking supplements for both of those (stopped taking vitamin B awhile back because it started affecting my sleep for some reason) and they have also helped with my mood and motivation.