With those kind of times it's likely you're running too much for your fitness level and are digging a hole with 100 MPW. If I were you, I'd try to play a bit with the mileage. Have some big days, have some short days, have some high weeks and down weeks. Even mileage fanatics like myself are having an easy day here and there (I ran a couple times sub 2:20 for the marathon and do not have great speed).
IMO you should improve by a ton when you just do easy-moderate mileage, strides (and sometimes 2 - 3 miles of fast and relaxed 200 - 400s) and incorporate 1 tempo per week of 3 - 4 miles averaging roughly 90 - 92 % speed of your 5k time on the day or 6 - 10 miles at roughly 88 % speed of your 5k time in that day.
You are likely underdeveloped in terms of speed, muscular endurance and aerobically and it's important to hit those three zones: Speed (really short stuff), threshold (tempos), strength endurance (normal and progressive runs). The other stuff is more like icing on the cake.
Pikachu