I run into this a lot -- someone tells me that they're blocked so are writing X number of words per day. The brute force method CAN work, but often it just results in page after page of drivel. If you're consistently frustrated, step back to figure out what are your problems.
Take a writing session to make some progress. Start your session with this sentence: I'm having trouble with this story because... then write your thoughts quickly. Talk to yourself. Is it that your story isn't holding together? Your characters seem flat? You're just bored with what's going on?
Now make a list and choose the most important problem to start. Take a day or two to go through your writing library to see how other writers have handled this problem. Solve it. Then move to the next.
Remember that writing lots of words is a laudatory activity, but repeatedly banging your head against the wall won't help you. Work smarter, not harder.