Listen to your husband!
You had your baby 3 months ago, and it took 9 months for the abdomen to grow and stretch to accommodate your baby. Give it some time and be patient.
The most important thing to focus on is your nutrition. Make sure you are eating enough calories and being smart about what you're putting into your body: clean, nonjunk food. Basically, if you shop the perimeter of your grocery store and eat fresh fruits and (most) veggies) along with whole grain products and lean/low-fat dairy and meat choices, that will help. Limit (not eliminate, but make them occasional treats not daily staples) white foods: pasta, bread, sugar.
The other thing you can focus on is your cardio workout. Make sure that you are performing cardio work that gets your heart rate elevated into your target heart rate zone and sustained there for 30 minutes.
You can do all the crunches in the world, but all that will do is strengthen your abs. Also, I second the advice mentioned by the previous poster that recommends the Tupler techniques; there are many abdominal exercises that, if you have abdominal muscle issues related to pregnancy, will only make the bulge look worse! Finally, you can do all the abs in the world but if you have a layer of fat or saggy skin over the abs, you won't be able to 'notice' them.