After Lunch Sleepiness Syndrome

It's at it again. Lately, after lunch I've been feeling sleepy and fatigue easily. I've not felt drowsy after my meals for a while now but it's been happening again. This is despite that I've been controlling the amount of food I eat by ensuring that I eat just enough. I had also ensured that I sleep early every night.

With the problem, I feel that it has been affecting my work. Now, with me being based at my client's office, I can't take a short nap when I'm sleepy like the way I used to. Oh... that feeling!!!!! I guess anyone would know how it feels like when you really wish you could sleep but couldn't. It's indeed a suffering. Anyone has got a remedy to this?