Has he lost interest/?

It honestly could be because of your new image, obviously you probably have weight gain and things down below aren't the same anymore. But my true belief is that you guys just had a baby, that can be very stressful, even though he's very happy about it, he could still be worried about all kinds of things. He probably is also very tired, if he's working long hours trying to provide for you and your child, then come home to a newborn, it's exhausting. Just give things more time and everything will be ok. The more you pressure him about it the more he will feel stressed and make it even worse.