Q: I’m dragging around with no energy these days. I never used to feel this way. What could cause me to be so tired all the time? I am 47 and in pretty good shape. — Kevin G., Milwaukee A: Chronic fatigue — that’s what being tired all the time is called — is something that 20% of folks ages 45 to 86 contend with according to a study in BMJ Public Health — and around 60% of those folks haven’t been able to pinpoint the cause. What we do know is that fatigue can be the symptom of many things, from sleep apnea and insomnia to hormonal changes, depression, stress, drinking too much, being sede…