You may want to ask your doctor, especially since you said you had a rush of bright blood. I've only had that happen once to me, and it was five days after my c-section with my son, they said mine was caused by a small clot, but it was all dark "old" looking blood, not bright red...
I think your system must be a little confused - being up and down, after being used to the Depo then getting used to you not being on it, and back and forth. So it could be a reaction to all that.... or, it could be signs of a m/c. Either way, having been on the Depo for b/control myself in the past, and subsequently having problems TTC after it, if you are planning Baby no2 in a few months, I would steer clear of the Depo completely, and use a less harsh means of b/control. I have heard of women who cannot concieve after a year coming off Depo who have children already etc, pointing to the Depo as the reason TTC has failed. I really think it can mess up your system as it is a harsh means of contraception and can hang-around in the body for a long time after.
I agree with Kate535. i was on depo for 2 and a half years came off in August 2007 and was ttc until August 2008 with no joy my periods were VERY abnormal one month they would be heavy then light then not at all, it was very emotional and depressing as i couldn't understand why my body was in such a state. I then decided to try bc pills for 4 months and my period has now been regular since January of this year, in total i have been ttc with my first child for 18 months and still nothing
If you are ttc in the next few months get off of Depo NOW and give your body time to clear from this poison. Best wishes to u!!!