Not wanting to state the obvious or repeat what other have already said, but I think January is always a tough time of year (in the UK). I've been hosting 8 years and have a close to 100% occupancy for the dates I want to host, but I always have to work that bit harder to make it happen in January.
Being aware of this, I keep it in mind quite far in advance. I keep an eye on my local competition, and set my pricing very competitively, with an aim to get a longer stay booking quite far in advance. I accept my actual "profit" will be minimal due to this. I'm happy if I break even in January, and taking this approach I always do.
This year I've had only one vacant day in January, with two bookings making up the 30 days, so I'm very happy.
December was definitely the most difficult month I've ever had. I really had to work to get bookings, at a time when I normally have no problems. The cost of living crisis is definitely hitting consumer spending, so I guess it's no surprise. This is likely impacting you too, amplifying the usual quiet January where everyone is broke following Christmas and clinging on for dear life for pay day at the end of January.
Be aggressive with your pricing, and keep updating with an eye on your local competition. View January as a month where you just want to take money in. Your profits will come at other times.