What are some things that could happen?

I'm 30 weeks pregnant with my second child. This child is a boy and I have a 2 year old daughter. My daughter was born about 2 1/2 weeks early via c-section and weighed 8lbs 9oz! Babies born in my family tend to be huge- I was 9lbs, my sister and brother were almost 10lbs. My grandma had twins and one was 8lbs 3 oz and the other was almost 8lbs...so as you can see, big babies run in my family! My 2nd pregnancy is a little different. I feel and look like I'm due next week, not in 8 weeks. My belly is huge and I couldn't be more uncomfortable. My back is killing me, my joints hurt and generally my body feels like hell. I haven't gained a huge amount of weight and I'm not diabetic. A few days ago I went to my 30 week apt and told the doctor that I just have a feeling that this child is A LOT bigger than we know and that I feel like I'm about 37/38 weeks, not 30. She measured me and said I'm measuring about 4 weeks ahead and scheduled me for an ultrasound to see how big this baby is in 2 weeks. What can happen if they do find out the baby is a month ahead? Will more tests have to be done to make sure? Will I have him early? I seriously don't think I can be pregnant another 2 months. My body won't be able to handle it. Also, I'm having this child c-section, that's what I had for my daughter, although nothing has been scheduled yet. P.S. They have not found anything medically "wrong" with me either. Help!? What could happen?!?!