My first sale was after six rejections, but it turns out that I sold the story to a not-very-reputable market that, in hindsight, probably took a lot of crap. Oh well. At least I got mine in before they stopped paying writers (and started *charging* them to "feature" their story!!).
The most rejections I have for one story so far is thirteen. It turns out that after leaving it alone for six months and finishing a master's degree, I realized it was pure crap. It is currently being re-written, and I'm receiving positive feedback about it from my crit group so far.
Not including the three stories I have out on sub, I've made thirty-five submissions over my lifetime so far, and all but one of them have been rejections. I'll admit you're ahead of me (congrats, by the way, for writing so many stories and making so many submissions!) but here's my secret so far for not getting down:
I celebrate my rejections. (No, literally. I get very happy and excited about where I'm sending the story next). Every rejection means that I'm putting my work out there, I'm doing the writing thing, and that I'm learning. Eventually I'll find someone who wants those stories. Meanwhile, I write more stories. When I finally start getting acceptances, I'll be able to gauge where my writing skill lies at the moment. Until then, I just have to have faith that I'm going to get a little better every time I write something new or fix something old.
And yes, I do get impatient. I've just learned to focus on writing new stuff instead of worrying about my ones on sub.