Feeling my baby on side is hard on my stomach the other is squishy?

I am 6 monthes pregnant with a baby girl:D I was feeling her kick so I was gently squishing my tummy and the left side is hard and the right side is not as hard kind of squishy. I felt kind of a round thing under my skin kind of close to the surface. I was wondering is that her head or lol. or was it like my uterus or something. She kicks pretty low and she kicks a lot. How do i know what I am feeling for? or waht i am feeling right now she just kicked and it was on the right bottem side:) i love being pregnant!