10 miles in 1:45 is pretty much where I was about a month or so ago (including the really exhausted bit!). You've got ages if you want to a marathon next year, I'm doing one in under 5 weeks as my first.
Just get on a 16 week plan like the ones on here, I started from practically zero running in the preceding 24 months (5 or 6 sub 8 milers total training and the GNR last year, that nearly killed me in 2:09, then nothing until this) and can now run a fairly easy 20 miles in training in around 3:30 but it was hard getting there and took a lot of time doing slow long distance runs which seem to be the trick. I noticed even walking for long sections of the long slow run to recover still massively improved my endurance week on week as it seems to be time on your feet moving that matters, not the speed.
The biggest thing I noticed while training is that my endurance increased (and speed) significantly as I lost weight - if that is an option for you. I'm over 10 kg lighter than when I started 11 or 12 weeks ago due to decent dieting and sticking to the training plan (6 ft and 94kg to 84 kg).
The other key thing is to book the marathon now so you can work toward it, keeps you motivated, especially if you book a 5K, 10K, and half marathon along the way so you know where you are up to.