On Depo Provera and Worried

I've been on Depo Provera for around five years now. I no longer have my period, haven't had it for pretty much the whole time I've been on Depo. I never get any other bleeding either. This morning, I found I was bleeding, bright red. So, I used a tampon, and tonight it looks like the bleeding turned to brown and then stopped. I probably wouldn't have worried about it as much as I am now if I had not just started taking Nuvigil (armodafinil) 150mg. In the drug info for Nuvigil, it states that Nuvigil decreases the effectivness of hormonal birth control methods, including shots. A couple of years ago, I took the drug Provigil (modafinil) and it said the same thing in its drug info. I asked my doctor at the time if this would be cause for concern, and she told me that she double checked with the drug rep and I had nothing to worry about. She didn't tell me to use extra protection or anything. Now, knowing that Provigil and Nuvigil are basically the same drug, I didn't think too much when my new doctor gave me samples of Nuvigil. I'm worried that my previous doctor was wrong, and that the bleeding is a sign that the Depo in my system is being reduced. I hate condoms, I've never used them, and I really like the low-maitenance factor with the Depo. I don't want to switch birth control methods, and I am functioning so much better now that I'm on Nuvigil. Do I really have cause for concern here?