I agree with pack a back and go straight there. Once I get home I don't want to leave again! But if my bag is packed with me then I am much more committed to going. I take a clementine or protein powder and eat/drink on the way home.
I also like the suggestion of getting more sleep. Your body heals and detoxes while it sleeps so really need your sleep.
Maybe you can find a buddy to help you--even if you don't go to the same gym. The girl who sits by me is motivated when she sees me bring my gym bag. If she doesn't feel like going, she tells me and I can always talk her back into it. Or create a Spark Streak to keep you motivated in consecutive days going or meeting your calories burned for a certain amount of weeks in a row.
Taking music you really like can be helpful for your mood while you're at the gym. I have my regular playlist and then my "gym" playlist of upbeat songs only. Spark even has some songs you can use.