Depo Provera and No Period

I've been on the Depo Provera shot for about 3 months now.

I know that it stops the ovaries from releasing eggs and that it also thickens the uterine lining. Since I have been on the Depo Provera shot, I have not had a period. I know that this can be the case for many. My question is whether or not the lining of the uterus is still shed, even if I do not have a period.

I have had some cramps today and have just discovered a brownish discharge. It's more like spotting. I've read that during the period, the cramps are from the uterus contracting and pushing out the lining. Could this be the uterus shedding its lining? Or could it be something more serious?

I also wonder: How is it possible to become pregnant if your ovaries are no longer releasing eggs? Is the shot safe enough to have sex without a condom? (Not that I will, I'd rather not risk it.)

[peekawho]

Its very common to have irregular bleeding or spotting while on Depo.  Or not to have any period at all.  
If you do not have a period, the uterine lining is not shed.

However, Depo Provera does not thicken the uterine lining.  It works by inhibiting the hormones that stimulate the ovaries to produce eggs.  It can thicken the cervical mucus and making it harder for sperm to penetrate, too.

You do not need to use condoms while on Depo, unless you are doing so for STD protection, or just feel the need to be super, super careful.  Depo is about 99% effective at preventing pregnancy by itself.

[Chata72]

Ah, then the website I read was wrong.

Thank you for clearing that up for me.

And I'm happy to know that my birth control is that effective.