I know exactly what you mean, you feel great when you wake up and it's like the day manages to grind you down.
You know it's coming so be prepared. Maybe an afternoon snack would help. A cup of coffee but beware of getting too jacked up on caffeine.
Have a plan for the day, an exercise routine, or maybe an AA meeting, plan out some errands.
AA made it much easier than I thought it would be to get sober. I would never have thought so in a million years, I went as per my lawyer's instructions, but I usually felt much better after a meeting in those early days.
During the day I look foward to a run. There is like a trust we unwillingly build in alcohol. Like I know I will feel better quickly if I drink. I've built that trust in running. I daydream about how I will feel after a run. If your brain insists on daydreaming about the drink just fast foward the daydream to the misery of the next morning. Remember why you want to get sober, don't compromise anything with your AV, your AV wants it all so don't believe any bargains it will offer.