Diet diet diet. Our natural enzymes and overall absorption levels reduce as we get older and we're more susceptible to gut problems, but also a number of other issues that lead back to these. Rather than treat / mask the symptoms with antacids, it's better to recognise the cause ...
We have recently overhauled our diet radically and I can't even begin to tell you how much more energy I have. The mid afternoon tiredness is gone, even at 10:30pm last night I was still bouncing around. My skin is soft, my daughter's eczema has cleared up, and heart burn is a thing of the past. We've cut out anything processed and are eating 70-80% fruit and veg. Dairy and gluten have been reduced massively and the other day I succumbed to some fresh bread and it felt like concrete in my stomach for ages afterwards. Sugar has been massively reduced - it has no nutritional value - and salt also. I've been completely radical on this but you don't need to go to such extremes to see benefits. Try eliminating key food stuffs to see what is your trigger.
Hope you get it sorted,
GG x