hi hippo -
I know this is continuing a discussion from 24 hours ago but one of the factors you should account for is that you may well not be rested enough to get the best out of your speed sessions, especially given your exhausting work patterns. another reason why you shouldn't be giving yourself a hard time. you're doing them, which is great and you should feel good about that.
also, do you remember to hydrate properly? I find it's a really good idea to take 500ml of sports drink along to interval sessions and get it down regularly. it does make a difference.