You couldn't match anyway (you can only go thru the match once). There is a website that lists open residency spots for PGY2's and beyond, but I can't think of it now. Im sure someone here will post it, but I'd start by talking to your PD and looking there.
This is not true. In fact, to get a PGY1 spot you would have to go through the match, or the scramble. I don't know if you can sign up for the NRMP now (in order to submit a rank list and scramble). The other thing to think about is if you really want to go to a program that ends up with a scramble spot.
You will likely need to start as a PGY1. They might give you some credit for your ob/gyn months, but likely not much, and any off service rotations you do. You should start by looking at the EM residency governing body website (not sure what this is) for requirements for going in as a PGY2 to see if this is possible.
Next I would talk to your PD and let them know they are going to have to replace you soon! Then talk to the EM PD at your hospital. This is probably the best way to get a spot for next year. Sometimes they can fit residents from other programs (but the same hospital) in somehow. They will also probably be able to help you navigate the process. It is very common to switch, and the PDs will be your best resources.
Good luck with everything!
Do not submit a match list. To match into an ob program with intentions of leaving immediately is completely unfair not only to the other people hoping for a match spot but for the entire program you match into.
It leaves the program in a lurch trying to find a candidate mid year and it gives them a reputation of having "residents who leave mid year" which can make it more difficult to match good candidates the following year. No one sees that you came into the program with the intention of leaving because you had decided to do ER before you ever matched.
As far as not wanting to go to a program that has to scramble; there are tons of good programs that are in the scramble every year and if you are flexible on where you want to go it shouldn't be a problem.