Mocks in January and I’m bricking it!!

I had my first day back in year 13 today. Things were weird with social distancing measures etc but overall was okay. I have no lessons on fridays so I had a fairly unproductive day, just a few free lessons. I couldn’t get wifi and had no textbooks so struggled to do much independent studies. Instead I sat with my mates and had a catch up. The common room is swarmed by the massive amount of year 12 students. Our sixth form has never been this big for such a small school. To put it into perspective last year there were a total of 20 people (y12 and 13) and this year there are 45. Its difficult to get a seat let alone study in peace. Also we are only contained to a small section of the school so there are very few empty classrooms available to use instead.
We learned we have mocks in January and there was an emphasis on how important these results could potentially be if there were a local lockdown during the final exam season and they real thing couldn’t be sat. I’m so worried as we have so little time and I’m already so behind due to lack of teaching during lockdown. I tried my best to take my learning into my own hands but some bits I just couldn’t do without teacher assistance and they all seemed to stop caring part way through lockdown. On top of this, I already have an issue every winter with regards to health and fatigue. Around late October I to January I will become in a state of constant fatigue and it impacts my ability to focus and study effectively. This period in all my years of school as always been my “break” period in that I am not studying to my full potential just due to lack of energy and an inability to sleep. I take iron supplements and am gonna get some vitamin D tablets but I’m worried about how much of a challenge studying during winter/ Christmas will be for me. Any advice on how I can maximise studying and reduce fatigue? I try to maintain a good diet and drink plenty of water, going to bed on time and waking up at a good time too. I don’t know what else I can do.