I had very similar. Gp put it down to depression when I really felt it was more physical. I do get depression, but this was different. They did a number of standard tests but also found nothing but low white cell count. They refused to test in relation to glandular fever or lymes disease. In the end, my mental health did suffer, body and mind are inextricably linked in health and wellbeing, but I believe it was more a consequence of an undiagnosed, untreated physical illness causing a low mood. I ended up off work long term and ‘cured’ myself by taking total rest for about a month and a half and building up mentally and physically again veeeeeerrrry slowly. A kind of ‘graded exposure’ approach. Part of it was a shift in mental attitude, becoming positive that I would recover if I was determined to, and partly by stopping from being over- sensitive to symptoms. Eg another cold/flu was just another cold/flu, back off a bit for a week or two then carry on building up, and not a sign that I was never going to get better. I stopped ‘training’ and just did physical stuff for the pleasure. No other goal than enjoying myself. It took about a year in the end. Good luck.