Erm... for me, this past year, I've been unmotivated at the very beginning of the semester and it's just been more difficult as the semester wears on.
It's not just because I am stressed and anxious over deadlines and assignments, but because my actual classes are not very interesting. Strangely enough, I am used to getting some kind of self worth out of my studies, and I even look forward to them sometimes. Since I've started grad school, however, I've been feeling nothing but dread. I'm just not adjusting very well.
As for advice... I always make a schedule to follow. I think of it this way: if I section off the stress into little pieces, it makes it easier to bear, and it keeps me from procrastinating as much and freaking out when finals rolls around. So I might look at planner and set goals for each week. It helps me, anyway.
I've been awful about attending class, but I try to make myself attend anyway. Some classes are so boring I'll bring my computer and surf the internet while the teacher is talking. It's not exactly polite, but at least I'm physically present so I keep my attendance points, and I catch it if there's a change in the syllabus or for a test. For a few of my classes I come to class an hour late, but at least I'm there for part of it. It's not... ideal, but it's the best I can do some days. It's better than never attending class at all, heh.
Also, if I can, I'll set aside one day, every week or every two weeks, where I ignore my homework and just do something fun and relaxing. I don't know if you have time for that, but it might be worth it. I find that if I let myself have a day without worrying about school, I can come back to it in a better state of mind.