Jen, what were you doing at the gym? Weights or cardio or both? For the cardio, I'd treat myself as a beginner, though if you were doing a lot, you'll be back in shape faster than if you were a total non-exercising beginner. Same is true of weights, your muscle memory will bring you along faster than at the beginning. I recently had 3 unintended weeks off from lifting (due to a nasty respiratory thing) and found when I went back I could do most of my lifting at the same level.
Cardio was another story however, and I'm still regaining my levels there (been 2 weeks back now).
I hear you though - take the weight loss and be glad. And get back to the gym and get strong. Good luck.