Negative

So I am on the depo have been for about 8 months now. The first 6 of those months I had full blown periods all month. Everyday. Well end of August was my last period. I've been taking pregnancy tests because with my seizure medicine it can decrease the depo from actually working. And it keeps showing negative. But I feel like some flutters in my stomach every now and then. I'm just wondering has anyone been on the depo and gotten a negative but was actually pregnant? I didn't know where to post this.