Another thing to think about, inline with the last few comments, is that if you have 45 days worth of muscle memory you might just be doing too much too soon. 20 miles where I live in the southern US, this time of year can be taxing with the heat even if you are a career commuter. That said until your body gets used to restoring itself in between rides you're going to drag. And when you get worn down your body wants to just diesel in a lower gear.

Its just my two cents, but I'd recommend shorter distances, pushing a little harder over those shorter distances but in intervals. In time I bet you'll find that you are getting there quicker with seemingly less effort.