hi oldhamjames...low energy could be due to several reasons:
1) not eating enough food
2) eating too much of junk and empty foods like fried and sugary things
3) not drinking enough water as it causes dehydration
4) low vitamin D3
and B12 levels as they cause weakness
5) excessive weight
these are a few reasons to mention but i would suggest you to start eating small meals every 2-3 hours in small portions like a bowl of oats porridge for breakfast, 1 fruit and few nuts for mid meals, salad with lunch and dinner, avoid excessive carbs like breads/ rice for dinner.. have soups, salads and some grilled chicken/ steamed fish, drink atleast 35ml water/kg body weight, check your heamoglobin, vitamin D3 and B12 and take supplements for the same if they are low. also take some b-complex supplement post breakfast to provide energy. am sure you will see positive results. all the best!!