OB's competitiveness goes up and down in waves, and for the past few years has been super-competitive. Right now your application package seems pretty good, although I'm not sure what impact repeating a year played into the decision making process.
I was in your shoes 2 years ago, again, 6 open spots and 4 were at the same program, 2 were UCLA pre-lim spots. The key here is to decide if OB is really what you want. I was able to interview with Family Medicine at my school after the match, but could not bring myself to do that specialty, while other classmates who did not match for OB at my school did accept the Family Medicine offer.
The other option is to do a pre-lim in either OB or medicine. Some of the OB pre-lim programs do not fill until later, you just have to call each one. With medicine pre-lim, let them know that you are going to keep looking for OB programs, but set a date with them that you will stop looking after that, so they can count on you for the year. OB programs lose interns, as the Step scores come in and people fail, or family obligations make it so they cannot do the position. So look at Creog clearinghouse as much as possible, and have your letters of rec and your ERAS application with you at all times to fax.
The worst case scenario would be to do a year of medicine and re-apply during the match next year, and most programs would look favorably on a year spent well with medicine, shows you can handle intern year, and it will be a benefit for the GYN and gyn onc patients.
Good luck!