Could i be pregnant???????

I am a mother of a beautiful one year old, and i didn't know i was pregnant with her til i was showing at 5 mos, so i really don't know the signs... My cycles have always been irregular so i'm not looking at that to tell me. The last few months i have been unusually tired, and every once in a while i feel a tiny flutter, but then i have a cycle. And then another. But last night i felt a fairly big flutter jump in my stomach, and just now i felt one in my side. Could i be pregnant? Or could i just be having muscle spasms? Btw: every pregnancy test i take comes back negative, and that happened with my last pregnancy also..