Two thirds of the way there! At my prenatal check up I was 15 pounds up from my prepregnancy weight. I have a pretty good sized belly now! And my little baby should be 8-12 inches long and over a pound now. This week alone she should gain about 6 ounces!! Its not fat yet though, all those six ounces will be in bone, muscle, tissue and organ growth!
At this point both baby and you are probably going through a rather uncomfortable and noticable growth spurt which can cause you some back pain. Warm baths, massage and moderate exercise should help with your back pain. Watch your posture carefully and if you are having a lot of pain you can try a belly support belt to try and get the weight and pressure off of your back.
Heartburn is probably also rearing its ugly head around now, your uterus is pushing everything up and that can include your stomach. If this is a problem for you try not to eat or drink too soon before bed and antacids like Mylanta or Tums are safe to take in pregnancy.
You may also suffer from constipation- a few easy things to try is moderate exercise, a good daily walk will help keep things moving. Lots of fluids will help as well and lots of fiber from fresh fruits and veggies can be helpful as well. Bran cereal is also a good help but if its really a chronic problem you can take fiber supplements. If all else fails talk to your doctor about it.