Lots of screenwriters are fond of the Field of Dreams quote "Build It And They Will Come" - and good on 'em. I truly believe that if you keep going, no matter what, one day all will come good. I have to believe that, as it's pretty much the story of my life, not just screenwriting.
"Build it and they will come... " Is it actually 100% true?
Yes. And no.
Common sense dictates that if you keep going, something has to happen for you eventually. But by that same token, common sense also says there are no guarantees either.
So instead of wondering IF it will happen for you, consider yourself a success ALREADY.
That's what I said.
If you are writing, never mind about the sales; there are many people already jealous of your success at just getting words on the actual page. Never mind saying you *only* placed in a contest, or you've *only* got [this number of credits] or you're writing TV when you'd rather write features or novels or whatever. Creative people are put down by others in society left, right & centre; let's not put ourselves down AS WELL.
If you're writing, you're a writer. You are a success. End of. Liken screenwriting to the notion of Pascal's Wager, but instead of imagining God exists, imagine that elusive notion of "screenwriting success" exists for you instead. Let's call it Lucy V's Wager!
After all, you have absolutely nothing to lose and absolutely EVERYTHING to gain.