I don't know if it's normal, but with your doctor's ok, if you aren't already, start some light aerobic exercise, just a treadmill. Smoking and sugar can affect energy levels. Eat healthy meals. Get outside and around people.
Recently I went through several months of seasonal affective disorder. It is pretty much gone with the better weather and sunshine.
So many factors can come in to play, any other health problems, lack of physical activity, diet...
For many people after the first few weeks or months are more energetic and fit.
A lot of areas to look at...but easy does it.