Check out this week's weekly training and racing thread. There was a discussion of my near burnout before Chicago 2015. You are just about where I was in the training cycle when I made my adjustments. My issues were more near burnout than injury, but I think the advice is still applicable. Below is an excerpt that might help you get your head back into a good place. Note in particular the 5k race differential that I mention.
_____________________________
That was part of it, but it really was a little bit more than that.
First off, this was uncharted territory in terms of volume. I had not even topped 55 miles in a week in the period from maybe 1995 until 2014, and even back in the early 90s (when I started running), I was usually a 40-55 mpw guy and can only recall 3 weeks in college over 70 miles (which ended with an injury). In my only marathon prior to that Chicago cycle, my three peak weeks were 76, 79 and 80 (over my original planned cap of 70).
Secondly, and more importantly, I was starting to struggle in workouts. The workout for the week in which I hit that 100 mark was aborted early because I wasn't feeling it. The following week, I had a workout that called for 8 miles easy followed by 6 x 1 mile with a minute rest. I had averaged about 5:19 on those for the same workout in my prior cycle, but this time around, I was up just over 5:31 for the 4th mile and then took 3:00 rest and struggled to run 5:25 and then took 2:00 rest and struggled to run 5:28. The effort was well above tempo effort. I then raced a 5k that weekend, running 16:09 four weeks after having run a 15:28.
At this point, I am now 4 weeks from race day and wondering if I completely overdid it and blew my training cycle. I decide to back off the intensity for the next workout, and not look at my watch (this is the 1000s at an in between pace referenced above). Then my subsequent workout was 13 at marathon pace, to be run in a half marathon setting. As mentioned above, I was trying to run 1:14:20 (goal marathon pace) and had a friend enter the race and run with me. This is a guy I had beaten as often as not when we raced. By the 10k mark it started to feel like a race effort, and then I faded to a 1:15:35 despite that race effort and got dropped pretty hard by my training partner.
At that point, it was pretty clear that I was not right and had to do something. I had to make a choice, and the best choice seemed to be to take my foot off of the gas, back down the mileage a bit and reduce the intensity a lot. Fortunately, it was the right choice and I ran a nice 2:30:52 for the male masters win at Chicago despite bad calf cramping issues the last 5-6 miles which required me to stop and stretch repeatedly (Deena Kastor, who I was with until 20-21 went on to run 2:27 high for a American masters record and the other guy we were running with (a guy I had beaten in NYC in 2014) went on tor un 2:28 low).
Sorry for the novel, but that should flesh out what lead to that bigger taper pretty well