Test when your period is expected if it doesn't show. If you get a negative and still no period, retest in 3 days. Everyone here loves Early Response pregnancy tests. You can buy a 3 pack at Wal-Mart for about $15.
I've been off Depo since March of 07 and have not been taking BC since Oct. They told me I should have another period at the end of this month which is when I've experienced all the bleeding. My husband didn't go in and get tested so we don't know if it worked. Also the bleeding I had was very light if it was implantation when do you think I should test.
Also after you get off the depo shot for a period of 2 to 4 months your periods are actually expected to be irregular since it has been so long since you had one. This is what my sister's doctor told her once she got off the depo shot. You could still be pregnant, anything is possible bur after the depo it is normal to have irregular periods and bleeding. Right when my sister got off her shot she had heavy bleeding for 2 weeks but her normal period last 5 days and is light light light and then she missed a month and then just had spotting but they said it was normal. I hope this helps you out a little bit
Implantation bleeding is usually just very light spotting for a day, maybe two. Not enough to even use a pad, really.
With a vasectomy and BC, your chances are slim to none. But God works miracles, so it is possible, I suppose. Your body could just be trying to get used to the BC.
If you believe you are pregnant or might be, you should stop taking the BC.