Hey Jack,
If I were you I would take a look at "The Intermediate" chapter of Practical Programming. I know that's not very helpful as a quick answer, but I'm not a coach and so long as you are self-sufficient enough I'm sure the answer will be somewhere in the discussion of the Texas Method, particularly phases 3 and 4 and the later discussion on back-off sets. It sounds to me like you've been training at very high intensities and increasing the volume despite this may be too simple an answer, but what the fuck do I know?
Best of luck Jack.