In my meanderings through the various writing groups I have joined, I always see writers posting celebratory messages like "Yes! I managed to write 500 words today!" I tend to snort in derision at this, as I can get through about 1,000 to 2,000 words in an hour on a slow day. When I get large chunks of time to write, I have been known to produce upwards of 8,000 words in a sitting.
But in truth, I have nothing to boast about, because the number of words doesn't matter even a little bit!
No one cares how many words I write--or how many you write, or how many she/he writes, etc. What matters is that you are writing, but your output doesn't matter at all!
If you measure your word count against the number of words someone else writes in a day, you're wasting your time. If you write faster than someone else, are you really a superior writer? If you write slower, are you really an inferior writer? The answer to both questions is "probably not".
Some of the greatest books in history have taken years to complete, and the speed with which you write has NOTHING to do with the quality of your work. In fact, if you're speeding through the writing process, it's fairly safe to say that you're going to make A LOT of mistakes.
No one is writing too slow or too fast--we are all writing at exactly the right speed. You cannot be discouraged because the writing process is slower than you like and you should never look down on slower writers.
Write at your own pace, and be comfortable with that pace. It is YOUR pace, and the fact that you are writing at all is truly what matters!