Avalon,
I think that when you begin to show can vary from woman to woman and pregnancy to pregnancy depending on a number of factors including genetics, diet, excercise, whether this is a first pregnancy etc. It doesn't sound terribly unusual to me to be starting to show at 3 and a half months. This is my first pregnancy. I hadn't gained any weight and didn't really start to show until I was at about 18 weeks. It seemed like my abdomen started to pop out overnight! I'm now at about 21 weeks, and I'm not huge yet, but I'm definitely starting to show now - my abdomen has grown a lot over the last few weeks. Hope this helps.
Kate