I was on Depo for a while and remember going for quite a few months without ovulating or having a period, its very normal (although frustrating!)
Atm, I'm on my 8th month of the pill and my cycle has still not regulated yet.
The only advice that i can give you is to keep temping and maybe go get some advice from a homeopath?
From next cycle I'm on liquorice extract (for my elevated testosterone) and Peony which works in combination with the liquorice to lower testosterone, balance estrogen and progesterone and "detox" the body from any lingering pill effects.
I'm not sure if the Peony can be used for Depo too but its definitely worth speaking to homeopath about (and its far better than any chemical drugs your GP would suggest!)
Hope your body bounces back quickly though!