Wow, so 14 with 12 GCSE's, you've been working hard, well done to you.
Personally, I wasn't homeschooled, but in Sixth form, I did waste my frees with my friends which was a bad decision on my behalf as I could've used that to study my weak topics, but this was what the smartest kid in my school would do.
Have a healthy and good breakfast.
Start studying at 8:30 and spend 2 hours doing a subject.
Take a half an hour break, and then spend 2 hours doing your 2nd subject.
Lunch break (40 mins) and 2 more hours studying your 3rd subject.
This would mean that you have been studying from 8:30 - 3:00. so 6 hours which is a lot. The reason for 2 hours focus and then break is because research has shown that our brain/mind loses interest in something (in this case a subject) when it studies it for more than 2 hours (actually it 90 mins but oh well).
Then around 5:00 pm start studying again but this time revise what you did in the morning. For instance, if you had done Maths in the morning spend 15-30 mins going over what you learnt, so that you can remember it. Research has shown that when you consistently go over something its more likely to stay in your long term memory, which is what you want since you want to do your Alevels in 11 year.
SO you would be done by 7:00pm and after that you can have the rest of the night to your self (preferably, go to bed by 10).
If you carry out this routine or an effective routine of your own, then kid you can do it. If you can do 12 GCSE's at 14 y/o then you can definitely do your Alevels in a year. Believe in your self, and work hard. Remain motivated, and consistent, don't give up half way, ask help when you're struggling and take good care of your health, exercise daily, go out for walks, don't waste your time, you can also give a weekend day to yourself as a reward.