Weak and tired is probably not an electrolyte problem. I’d say look at whether you’re eating and sleeping enough and get your iron checked
Iron deficiency and vitamin d deficiency can affect how tired you are/feel. As can having a baby and lack of sleep obviously.
I like the MyProtein lemon n lime sachets and I find they're really affordable compared to others on the market. Was not a fan at all of the lemon lime Liquid IV ones but that's the only flavour I tried