Get up earlier and spend some time right away working on your smaller things requiring focus. I don't think your core work day would be robbed of anything either, a significant portion of the energy loss is the context switch from work to commute to home.
If you get up two hours earlier and go to work at the same time, the end of the day will feel a bit latter but i'd wager you'll be just as productive as the end of a day right now.
Note: Speaking from speculation, not experience.
If you've got flexible office hours, pick a few days a week where you come in after lunch and work later. If you are worried about how it might affect your work, front-load the day with things that will take the most creative energy and save the evening for things like catching up on emails.
I don't know your details but this could be your mind and body telling you to change for the better. Do you exercise, do you sleep well (at least 7-7.5 every night). Do you have hobbies outside software? Do you get out and hang out? How's your personal relationships? All these things matter and if something is really out of sync your mind/body starts to fight you. Listen to it. The trick is to have a balance to your life and still get to where you want to go. Sometimes the balance shifts in one direction or another but it's always good to try to maintain the balance.
15-20 days - really motivated work 10-12 hour days 5-8 days - motivated but uninspired 4-5 days - completely unmotivated and uninspired
that is pretty much my typical month, every month. the lows are low but the highs are high. just find your groove and stick to it. everyone becomes unmotivated at times.