Weird feeling in pelvis?

I think I populated on the12th or 13th so I'm....8 or 9 DPO. For the past few days I've been get this weird sensation in my pelvis like there's something in there pushing on my uterus/bladder. It gets more noticeable when I cross my legs. It's hard to explain, like there's a balloon in my pelvis. It doesn't hurt, it's just...there. Anyone know what's causing it?(learn more on Glow: https://glowing.com)