I am by far no expert, but I would say that you just aren't getting enough calories. Perhaps you should add an extra 200-300 calories on days when you do such a grueling workout, so your body doesn't go into starvation mode. And make sure you're drinking enough water! (nothing specific, I just think it's always a good suggestion

) Your efforts seem so dedicated, you'll bust through this in no time!!!
Hang in there!