It could certainly be a rupture. That's kind of what it felt like with my first, slow leak at 36w6d, but it didn't stop for the next 20 hours. Then, labor started. If you in fact do have a leak, it's not anything to worry about, really. Labor will start eventually! BUT, if you're nervous, I'd go get a NST at the doc tomorrow. I wouldn't allow another vag exam because now is the time when exams have the greatest potential for germs. And THAT is when the clock starts ticking on when they want you to have the baby. No exams, no worries.
and drink a LOT of water! Your fluid will replenish itself. Labor may not be imminent, and if your OB doesn't freak out, you could go on like this for a couple weeks! That may not be what you want to hear though, but it's honestly ok as long as you're doing kick counts, and keeping yourself very hydrated.
best wishes - and get some rest now!