This is going to sound really stupid, but get bloodwork done for a vitamin deficiency. As one ages, nutrient absorption wanes. You often need more, to get the

This is going to sound really stupid, but get bloodwork done for a vitamin deficiency. As one ages, nutrient absorption wanes. You often need more, to get the same as when younger. So even with an unchanging diet, you may have changed. Working out is the same, eg a 30 minute walk may require a 35 minutes, 40 minutes, for the same cardio benefit.