It takes 6 - 12 months to change your body.
nytimes.com
nytimes.com
Now I'm "back on the wagon" so speak, going to the gym daily (though only once) and it is very slow going to gain my strength back. I lost 40-80+ pounds on every lift and much of my stamina as well. It is very demoralizing, so I recommend that if you can get into a regular exercise habit, for god sakes, stick with it! It is so much harder to form the habit than it is to break it so you must be very vigilant.
As an added bonus tip, anybody who tells you that going to the gym "a few days a week" is always enough because of muscle fatigue and so forth is an idiot. Segregating muscle groups properly and using the bare minimum of supplements allows you to go at least every day. Personally, I feel as if once a day isn't enough to accomplish much of anything as I am forced to split my days between weight lifting and cardio to achieve any sort of balance.
Edit: replace "every day" with "6 days a week"; a day of rest goes a long way.
I'm not convinced by that; if you are going heavy on major compound exercises (e.g. squat and deadlift) you will need CNS recovery at the very least. Right now my programme looks like weights day, light cardio day, heavy cardio day, repeat, rest day, back to beginning. That's only 2 weights days a week but believe me, that's plenty.
Combined with a high-calorie (balanced) diet and supplements, I was able to make consistent gains week-over-week for the life of the program. In the beginning it was more difficult as my body wasn't used to the work, but as time went on it got to the point where I was fully recovered in the areas I needed to be to complete the day's routine with more weight than the previous week's iteration (each day was a separate routine).
I plan to stick with this 'til the end of February then adapt it to prepare for a Marathon in May.
Since you're preparing for a marathon it seems to make sense to focus on lower-body and mainstay complex exercises (squat/deadlift), but I am unfamiliar with that specific sort of training so I can only speculate.
As mentioned, you seem to have an exceedingly high volume, especially considering the narrow focus of your exercises (at least one day 1). Your rep count (5) suggests a focus on raw strength, but the set count (5) is more common for endurance.
My objective right now is to improve core strength and relative strength, then in the 3 months leading up to the Marathon to shift a bit more towards power-endurance (e.g. Tabata, Fartlek, weekly long run). Previously on half-marathons I've really lost my form towards the end, that's just wasting energy needlessly, especially on cross-country. This time I'm going to keep it tight all the way.
In my opinion they proved that random subjects cannot stick to an exercise regiment assigned to them by researchers...