Rest.
More info tomorrow, but rest. If you run, then short 3-4 miles runs2- 3minutes sleeper mile than intended pace, but with 1 mile at race pace in the middle. But I would only do 1 of these
EDIT: SO the issue is you have basically done a race within training. It can take weeks to recover from a race like a half marathon. If your target for a HM is under 2hrs and you ran 12 in 1:44 then that was when you had your race, you should have saved that effort for race day.
The distance itslef is fine. For a HM it is good to get runs of 14 to 16 miles under your belt. But these should be at a pace 2-3 minutes slower than you intend to race at, as should almost all your running. These are harder effort also need to be around 4 weeks before race day so you can recover.
Not much you can do about that now. Extra sleep and reduce stress will help. Swimming or walking will help active the muscles without stressing them. You can also do some massages.
You have to realize there is absolutely nothing you can do between now and race day that will help with fitness or your ability to race well. Useful adaptions takes months, or even years of training. However, there are lots of ways you can screw up and ensure a bad experience. Number 1 would be to go for more long runs. They will do absolutely nothing for you at this stage beyond damaging muscles that wont repair fully by race day.
Once your legs feel better then I suggest doing 1 or 2 runs of 3-4 miles. Perhaps if you feel good this Thursday-Friday something up to 5 or 6.. Do 1 or 2 miles at 11:30 pace, 1 or 2 at 9:00 pace and 1 mile or so at 11 pace, given you want to run at around 9min/mile on race day.
2 days before race day something like 2 miles with 1 mile at 11:30, 0.5 to 1mile at 9:00, may being finishing at 8:45, then 0.5 miles at 11 pace. This will loosen your legs.
If 2 hours is you intended finishing time, then make sure the first mile is done at 9:40-10:00 pace, cut down 10-15 second a mile until you hit 9:00 pace. From mile 9 to 10 you can take stock and see about speeding up about 10-15 seconds a mile. Once you have a mile to go you can see about opening up more.
Thank you for your advice. My wife began running with me at the same time and we always run together. Our fitness levels are very similar. She found the 12 miler just as hard as me but surprisingly my legs are still tired, especially quads which is odd, she's fine!
I thought it was important to get another 1-2 long runs in before the day because we have only ever run 2-3 long runs above the 10 mile mark recently and felt we didn't have enough experience doing the distances. But from what I understand from your advice is that rest in the days I have left is far more important than doing any running.