Sounds to me like it may be baby moving! They say that you'll notice it more around 21 weeks, but that you could have felt it before, except that you perhaps thought it was gas, or like a series of bubbles pooping or that butterfly feeling!!!! I felt baby kick ever so softly just after 18 weeks, so I think it could be baby saying "HI" to it's Mommy!!!!!!
I asked my Doctor about it b/c I hadn't really felt anything up until 18 weeks, and he told me that I would start to feel alot more around my 20-21 week!!!!
I am now 19weeks, 2 days!
Hope all else is going well for you!