It does sound like low blood sugar. The blood sugar increases followed by insulin spikes is a viscous cycle that can cause low blood sugar, irritability, etc. Eat more complex carbs in the morning that cause a gradual rise in blood sugar. Instead of candy eat a banana. Simple carbs can provide quick energy but the crashes due to insulin spikes combined with exercise can result in low blood sugar and all the problems that go with in including fatigue. Might want to have a glucose sensitivity test to investigate this. An internist can arrange this. Hang in there a good internist can help you get to the bottom of this.