You are leaking colostrum. Colostrum is a clear-to-yellowish liquid that can be a bit thick and sticky, hence the crustiness when it dries. It’s the first milk your baby will drink for the first couple days until your real, regular white-ish-looking milk “comes in.” It’s the really good stuff, the liquid gold, so packed with antibodies and stuff that it’s like a Red Bull for your newborn’s immune system.
And yes, you start producing it while pregnant and MANY women will realize they are leaking it, and the leaking CAN occur pretty much any time. The third trimester is the most “typical” time, but it can absolutely happen earlier. I leaked in my third trimester with all three babies, just a little. BUT long before that happened, I would occasionally see if I could squeeze/hand-express anything and usually could by some point in the second trimester. So as long as your nipples seem to be otherwise normal looking and feeling (i.e. not red, inflamed, painful) and the liquid is clear and not pus (colostrum also…tastes very sweet, in case you want to check that way OH WE’VE ALL DONE IT), I’d simply congratulate your boobs for being early overachievers. (After you call your doctor and/or promise to mention this at your next visit, that is. As always, NOT A DOCTOR AND NOBODY SHOULD LISTEN TO ME EVER.)
As for being lopsided in production — I have NO IDEA if colostrum production in pregnancy is any “real” indicator of what your milk supply will actually be like once you give birth, but in case you are concerned: It is relatively common for one boob to produce more milk than the other. I’ve nursed three babies with super lopsided boobs — the right side was damaged during a cyst aspiration and I