How recently did you run your marathon?
(the resulting drop-off in pace usually lasts 4 weeks, but can last longer if you ran very hard and or did not recovery fully)
That aisde your week is unbalanced. To fix it will take a while, but is possible. I would start with:
1. Drop the swim/spin if you want to get better at running, keep them if you are happy being middle pack, you can add them back once you adjust to new mileage (if you want).
2. Remove the speedwork (not sure if this is all on the same day, but its way too much and it doesnt look like you are doing and specific speedwork for a specific event either).
Then you need to rebalance your week. Your LSR is long in comparison to the rest of your running and therefore will be overly tiring. That means you are doing essentially 3 hard sessions a week plus spin and circuits at the moment 
5 days a week would look like this:
Tues - 4-6 miles easy
Weds - 6-8 miles easy (replacing your 7/8)
Thurs - 4-6 miles easy (this will become your speedwork later)
Sat - 4-6 miles easy
Sun - LSR 12-14
Then once you have got used to that for 4-6 weeks you can start adding in some speedwork (which will be totally dependant on your next A target race in say 6 months time)/or adding more mileage - dont do both at the same time.
Thats what I'd do anyway