I maintain a spreadsheet of my submissions, acceptations and rejections. Call me anal, but it helps me keep track of when I sent something, how I sent it (email/postal?) who I sent it to (so I don't accidentally resubmit old material), and whether I've heard back from them or not (and whether it was a yay or nay).
I do this for both my short stories and novels. My cumulative submissions are well over 100...probably close to 150, including 20 agent and editor submissions for one particular novel that I've sidelined at the moment. I'm up to 15 agent submissions with the one I'm working on now, and so far, half of those are rejections. In fact, I've only sold about 5 short stories so far, and the other odd bits are contest winnings as well as requests for partials or whole manuscripts. The majority are rejections so far. It took almost four years before I sold my first short story. Then I got an agent for a novel, but that agent (who was wonderful during the time I worked with them) recently left the publishing industry for personal reasons, so I'm back to square one. No bitterness here, honestly. It just happens. I've taken baby steps and am getting a little closer every time, and I believe I will break in one of these days.
For now, I keep slotting entries into the spreadsheet. When I get accepted, I highlight the entry so I can immediately pick it out among the rest of them and remind myself that I'm technically a published author. I'm adding to my writing resume, bullet point by bullet point. Rejections always suck, but they're part of the process. Persevere.