heavy pressure

Victoria
I am almost 14 weeks with twins. I've noticed that I am having a lot of pressure on my lower abdomen, right above my pubic area. Is this normal? 
When I sit, it kinda twinges like a sharp but dull pain, like I have to pee but I don't. It's not on the sides so I know it's not the round ligaments it's right in the middle, where you would generally have menstral cramps.