@AdamS that is great news that you are able to do more...and it is totally understandable that you are thinking
about how much to do.
In my 20's I was very sick for about 10 years and then got better to about 75% of normal. Like those above I did push it too hard and kind of thought I was well, had ticked that box etc. ...I really pushed myself for years and then crashed big style over 3 years ago after repeated episodes of acute health problems turning chronic. I was on my own and abroad teaching TEFL so had to keep myself going...coffee, sugar etc...
I now function at 20% of normal in Winter and 30% in Summer.
If I have advice it would be: listen to what your body is telling you when it is NOT cranked up on alcohol, caffeine or sugar- it can be all too tempting to do that bit more with a few empty calories or caffeine giving you a rush of energy that you don't have. Alcohol is full of sugar too. As part of my pain management I set my alarm to go off every 2 hours and I check if I need pain meds and also how I am doing? Do I feel ill any symptoms? What is my body telling me- does it need rest/ lie down/ darkness, meditation etc.
I also find keeping a very brief daily diary has helped me to understand ME better...and I can flag potential problems earlier.
The other thing is that there can always be other things that can overbalance you- emotional situations, bereavements, moving house, infections, operations, pollutants.....all these things are out of your control...and probably will affect your symptoms.
Wishing you well
BTW: I also have POTS and take an electrolyte that has no sugar or sweetener
https://www.amazon.co.uk/gp/product/B00L7WXIFE/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1 I also eat every 2 hrs but not sugar!