Depo-provera - Facts?

Before I began using Depo-provera, I did quite a bit of research.

Upon receiving the first shot, I was under the impression that the drug would begin to work within 24-hours of the shot (at least, in the sense that I could have sex wthout worrying about pregnancy), as that is what the official site (depoprovera.com) claimed. My doctor herself didn't clarify exactly when the Depo would be fully-effective, but she informed me that it would work quickly and efficiently. I didn't think to ask for an exact time-frame.

When I recieved the first dose, though, I was told by the nurse who administered the shot that I should wait at least until my second shot to have unprotected sex, even though I did receive the first in the appropriate time window (within the first five days of my period). I was shocked, but when I questioned her, the only answer I received was that, "it takes time for your body to get used to the drug."

Today, I received my second dose, and was told, once more, that I should wait until my next shot. I have never heard of any form of birth control taking six months to become effective, and frankly, it startled me.

The nurse also informed me that Depo is not any more effective than birth control, while my research has shown me that it is nearly as effective as female-sterilization!

I don't understand. Every site and indivdual that I've consulted says one thing, while this nurse tells me something else. My doctor isn't in, since she's currently on vacation, but I'd really like some answers. What are the real facts about Depo-Provera? Does anyone have any first-hand experiences with the drug that might help me out?

Thanks.