Firstly : Have a physical checkup. Get the actual printout of the results, because just being told 'normal' isn't ok for some of these values (esp vit D and thyroid.)
Blood pressure, blood sugar, Hba1c, full thyroid panel (not just TSH) vit b12, ferritin. Full blood count, urine dip.
Check the actual results - many of us are deficient in vitamin D, if so take a vitamin D3 (not D2!) supplement. If yours is very low your GP will need to prescribe a much higher doseage.
If your TSH is over 2.7 ish request further follow up. If your ferritin is at the low end take a liquid iron supplement (don't take iron supplements unless you know you are low, excess isn't at all good for you.) megadose vitamins are best avoided unless prescribed - they can do more harm than good.
Check lifestyle- are you getting enough quality sleep? Go to bed an hour earlier. No screens an hour before bed. Use the night shift option (iPhone) or f.lux on android past tea time. Get up and get outside in the morning.
Excercise but don't overdo it if you feel run down. Brisk walks, aim for something that makes you feel invigorated rather than over-pushed.
Eat more veg and don't overdo the fruit (too sugary.) check diet - honestly how much sugar are you eating? No need to do any extreme faddy stuff, just cut down on sugar and processed foods and add in more veg. A good basic multivitamin isn't going to hurt, or a berocca or something. Probiotics are good too - yoghurts etc. Gut health is important
I'm shattered and run down after a difficult pregnancy, hyperemesis, and a non sleeping baby (now a toddler!) has left me completely depleted. I've had endless bugs this year so I'll be following my own advice!