all this talk of depo is weird... when i was on it (only about 6 months) i had the opposite effect, i never had a period. and even when i got off of it i didn't get one for almost 10 months afterward... (and i actually lost weight while on it though i don't think that was birth control related) lack of period made me a little nervous, but i wasn't having much sex anyway, so it wasn't a big deal... probably didn't ovulate that entire time either (you always ovulate exactly 14 days before your period) oh yeah, and sperm survives for several days, so you can have sex a few days before ovulating and still get pregnant.
oh one complaint i do have about birth control is with yasmin. i rarely, if ever, got cramps until i took it and i took it for about two and half months and got off of it, and now i almost always have cramps aaand..with depo they say you might bleed a lot in the beginning but eventually you wont have a period. just depends i guess... have you talked to your gyno about it? they would know better than anybody and can get you on something else if your body isn't liking the depo