Two things strike me: I used to have this problem (afternoon sleepiness) but I now have a big breakfast, and then a lighter sugar & carb-free lunch (otherwise I nod off - it's caused by an insulin spike after eating sugars/carbs) so, for example, rather than having a sandwich, I'll have a cheese or ham salad, with a big dollop of mayonnaise (the fat keeps you fuller). No biscuits or crackers or bread with it. Keeps me awake all afternoon! (I'm in my 60s). Secondly, I would also say get your thyroid checked. If GP says that your thyroid is normal, I would ask for the score and then seek a second opinion. The scale that the GPs use is low, and also what's normal for one person may not be normal for you - especially if you're only just in the "normal range". (I was told my thyroid was normal but then I saw a private doctor who prescribed thyroid supplement and that really helped - as well as cutting down on sugar & carbs!)
Our Welfare State. Is it broken?