7 1/2 weeks and showing... hard tummy, twins?

angela171717

I'm 7 1/2 weeks along and my belly is sticking out a bit. I was not super skinny before pregnancy (5'8" about 150lbs). Today I was filling on my bump, which is impossible to suck in already, and realized that it is pretty hard. I'm guessing that this is my uterus but I read that it wouldn't be expanding upward till later in pregnancy? 

 Has anyone else experienced this, this early? Does this mean I might be having twins?