Luckylegs, it's entirely possible you caught covid before any testing was available so you might well be suffering long covid.
I've posted previously that was my situation and, bizarre though it sounds, was actually pleased when I got a bad dose of shingles as it was recognisable, physical symptoms saying there was something wrong.
Current scientific thinking seems to predict a wave of long covid related conditions, which is bloody terrifying really as it's so random and can affect so many different organs - the most frightening being possible brain shrinkage with loss of function mimicking some aspects of Alzheimer's.
There really isn't a lot of help out there apart from non medical long covid support groups and your own research about it. One piece of advice that works for me, 2 years on, is pace yourself and please don't do too much.
It's so easy to think 'ooh I don't feel too bad today' and go at stuff as normal, especially if you're normally very active. You WILL feel it twice as bad the next day. And try not to get too down. It does make physical, chemical changes in the brain that can result in very strange, low moods completely different to depression.
It takes a long time but, in my case, I'm gradually getting better and, if it's any use to anyone I've been helped by a concoction I make of raw fresh ginger, apples, apple cider vinegar and, most important, black nigella seeds whizzed up in a nutribullet or blender. The black nigella seeds have a property that disrupts the virus' protein spikes making it less easy for it to get a grip in the blood vessel linings (the endothelium).
Good luck in coping with it.