May I suggest a handy dandy little device called Mirena. My sister has one. Fabulous. She can't take the pill without going psycho. This little baby does not flood your whole system with excess hormone in the same way that implanon, the Pill and the shots do. It just delivers it where it's needed, it has no long term side effects (that they know of) and it works.

http://www.fpq.com.au/factsheets_brochures/Fs_Mirena.stm

Best of all, if your GP refers you to family planning or you get them on a good day, its $20 for 5 years of no babies.