31 weeks pregnant with my first seems almost to big for my belly

I am 31 weeks pregnant with my first child who is expected to be here the 3rd of August. I'm having difficulty breathing and sleeping. She pushes out feet and hands into just about anywhere she can. Lately the kicks are becoming so strong they make me breathless. Other days her position hurts me no matter how I lay. I go in for another ultrasound on the 13th. On a note: my pregnancy belly seems on the small side women who are several weeks behind me are bigger. Is she just getting cramped and stretching to relieve it?