Normally, I never have simple carbs. I'm also usually tired throughout the day, but then I started having sugary stuff, which suddenly energized me again. I've been having a candy bar every day, and I haven't felt day-tired in weeks.
When I remember I substitute dried figs and prunes plus water with a dash of juice or weak cordial to flavour, works just as well and probably way better for nutrients and fibre.
In my experience, sugar high is temporary, and the longer you persist with a sugary diet, the more adverse effects will show. I felt the same way with caffeine too.
Of course everyone is different, and what you are doing may just be right for your body.