Generally speaking, it is very common for 100% recovery from Covid to take a long time. I have a good friend who has a PhD in exercise physiology and works with team GB athletes and she said several of their athletes have had long Covid like symptoms that have affected their fitness and particularly their ability to recover. I know that their approach to managing training is to give more recovery time between sessions and to limit the frequency of high intensity training, instead focussing of lots of steady state, zone 2 type training. I know it's sometimes hard to train less when you just want to make progress, but in this situation, I think you might be wise to drop the intensity for a few weeks to give your system more time to recover. In addition to this, I would really prioritise recovery. I'm not an expert in that side of things, but if it were me I'd be increasing calories and eating lots of nutrient dense foods, particularly those high in iron, zinc and B12. There are some papers suggesting that vitamin D is important for Covid recovery, but it's not the best data, might be worth a shot though and certainly won't do you any harm in the middle of January!