Difficulty writing, and what I need to do about it. (Suggestions are welcome.)

Lately I've been having a hard time sitting down to write. I've written about this before, I know, but it has since become worse, to the point of complete stagnation in my writing. As some of you know, I recently decided to shelve The Sometimes Sword, of which I was on the third draft. You can read about it here. I have started work on a new book, but I find myself wondering sometimes if I'm really cut out for this. I have always heard (and I have said myself) that a writer has to slog forward, and just do it. It's good advice for sure, logical and all that. But it misses an important point. What if you can't slog forward, because you can't seem to put your fingers on the keyboard? What if every time you sit down you feel sick, and ashamed? What if so many doubts clog your brain that you can't seem to recall any words other than self-recriminations?

Can I really call myself a writer when I let two, three months go by without actually, you know, writing? Thankfully as of today I started once more on writing the actual words of my new first draft, but how long will that last? How long until I look at what I've done and start hating it?

My goal right now, and it feels so inadequate, is to write at least once a week. This is a far cry from 5 pages a day like my last book. But with school and work I'm mentally exhausted every night. (I hate you Philosophy 1200.) It feels like writing would be a bad idea most of the time. I rationalize that the stress isn't worth it, that I as an adult can choose to do what seems to be the easiest thing in the evenings, and if that's not writing, then so be it.

Somehow, I know that's all wrong. I know it is. But it persists. Does anyone have suggestions, or even similar thoughts? I want to hear about them, and maybe what you are doing to overcome them.