If you are just starting your third year, you shouldn't even be thinking about postbaccs at this point.
Generally they are for two main groups of people: if you never took the prereqs or if you have a low gpa.
If you fall into the second group, you still have plenty of time to fix that. Do whatever it takes to get your gpa up!
Take fewer credits each semester if needed. Maybe if you took one less class and did some work over the summer or took another semester to get done, you could start banging out the A's.
Try to correct any problems now and if you are still subpar after 4 years, then start thinking about postbaccs.
The 100% admission rate at some programs has NOTHING to do with the program itself. They only admit excellent candidates who would have gotten in regardless of where they did a postbacc. These programs are for people who have a high gpa, but just never took the prereqs. If you end up with a low gpa, you will not get into this type of program. (bryn mawr for example).
