Your period doesn't really fully regulate until quite a while after your first one. It's not unusual for some people to get two periods in one month, nor is it unusual to occasionally skip one period. If you got your period a few weeks ago, then you may have another month until you get your period again.
However, the second bleeding you had, was it extremely light? There is such a thing as implantation bleeding, which is around the time you would have conceived a baby.
If you're concerned about pregnancy, then I would suggest that you get a pregnancy test. Wait until you feel you've missed a period (or when you should have gotten it) and then take it. That's what I would think.
As for spermicide, you said it yourself, it's not 100% thing. None of the contraceptions are... however, spermicide doesn't have as high a success rate as something like a condom. If you are planning on using spermicide again, I would consider at least to pair that up with withdrawal... though a condom (or birth control) would be better.