I'm going into my senior year of college, and I decided to enter the Pittsburgh Marathon, which is about 4 1/2 months away. Throughout high school and college I've run track and xc on and off, my best times are low-16s for 5k and 4:10s for 1500. Once on a training run I was able to do 14 miles in 1:34 without trying to run as fast as I could, so I'm confident with the right training I could go sub-3. This past semester I wasn't on the team and ran very inconsistently, about 20-40 miles a week. How should I go about beginning my training, what kinds of workouts should I do , and what should my peak mileage be to be able to break 3?
tl;dr - low-16s college runner wants advice to break 3 hours in the marathon