I think this is happening with you because of your irregular timings of work and sleep.
Our body have a clock that work with sun. So as sun sets, our body starts preparing for sleep. Working or eating or exercising after that will increase body's allertness and it get tired fast.
Next Steps
consult with me for further assestance with the issue.
Health Tips
try to change your shift timings.
if not,
eat dinner early and sleep on same time every day.
get up after 6 -7 hr of sleep.
workout after getting up.
Have berakfast like king, lunch like worker & dinner like beggar.