Hi D.,
Boy did you find the right mom to ask for advice! I do romance parties for women and deal with this issue on a regular basis so I know I can help.
First, as I'm sure you know, the day your son was born, your entire life changed. Your every day revolves around your new baby boy, and by the time you go to bed, you are exhausted. It is really hard to feel up to sex when you are tired so it's understandable. Make sure you are taking vitamins and are sleeping when the baby sleeps so you don't wear out. You'll find yourself much more into your husband when you're not tired.
Second, most moms find it difficult to do the things for themselves that they did before children, especially the things that made us feel sexy such as pedicures, bubble baths, and so forth. Make sure that at least once a day you do something for yourself whether it be slapping some paint on your toe nails or actually spending time primping.
Third, the center of your world is now your child, that doesn't always leave time for affection and closeness in a relationship. Where before you had all the time on earth to talk, and bond, you now have to work on it. Date night is the best answer for this... pick a night out of the week when you can get a babysitter then spend time with your husband. It doesn't have to be anything extravagant, it could be going for ice cream or window shopping. Just make it something that gives you time to talk and reconnect. This is important because sex is so mental for women. If you don't feel close to each other, sex is going to be the farthest thing from your mind.
Lastly, childbirth does some pretty radical things to a woman's body. Hormones levels fluctuate, and your body changes. In some cases, women lose sensitivity in their clitoris after childbirth, which can cause them to lose the urge to have sex. I recommend a good enhancement gel to bring sensation to it's peak, and remind you why sex is so great. Believe it or not, once you get the ball rolling, it will get easier. Having orgasms increases intimacy because the “cuddling hormone,” also known as oxytocin, is released in the brain and increases feelings of closeness and bonding.
Hope this helps a bit!