Op food can make or break how well you feel, you need to control your sugar,so to rule out anything more serious overhaul your diet straight away. My DF has had erratic blood sugar problems his whole life, it affects his moods/ energy/concentration/ vision...this is what works....
Breakfast, sugarfree museli/ bacon and scrambled eggs/porridge with blueberries.
Mid morning, ryvita with tomatoes and hard boiled egg/apple with almonds/blueberries with oatcake.
Lunch, fresh soup (tinned has added sugar, check this) wholemeal bread/ham and scrambled egg/egg salad.
4 pm snack,
piece of fruit, with nuts (essential to slow sugar rush from fruit)
oatcake with almond butter/ ryvita with avocado or cucumber/sweet pepper /cream cheese.
Dinner
lean meat or fish with 4 steamed vegetables, tiny amount of carbs ie one small roast potato, dessert spoonful of pasta or rice.
Roasts fine/bolognese/curries/casseroles/stirfries just very little carbs in the evening meal.
Berries are fine for dessert, strawberries and greek yoghurt, blueberries etc..
Tea and coffee fine (no sugar) avoid fruit juice and flavoured drinks all have sugar.Drink only water.
Avoid bananas, processed bread, baked goods ie croissants, cake, biscuits. (sorry)
My father is now 85 and still works 8 hours a day in his 2 acre garden, as long as he sticks to this diet with few exceptions he is well. He gets tested annually for high blood suga,r it has been higher than normal his entire life, yet he is slim and fit. Diet is the only solution.
If you try this for a month you will know for sure if this is your issue.
Good luck.