I'm not sure that I read the same original post as everyone else.
The op has gained 10 kg and doesn't feel sexy. She wears frumpy clothes and feels gross about herself. This really puts her off sex. Also, she's tired.
There's a secret I'll let you in on. Your husband doesn't care about your weight. He just likes it when you are naked and in a good mood. Honestly. Ask him. Most mature men are like this. The whole "only skinny women who've never given birth are sexually attractive" thing is a myth. Even men who buy into the myth when they are young figure out it's rubish as they mature if they are well adjusted, which yours is. Naked and in a good mood is all he is asking for.
Second, try buying a few new clothes or even Jammies or a teddy in your current size. Even though you don't want to stay this size, you will feel better about yourself in cute clothes that fit. Not doing so is punishing yourself for having changed when bringing a new life into this world. It's ok that you changed. It's actually pretty freaking amazing. You are a force of nature!
Finally, give morning sex a shot, or nap time sex a try (on the weekend, obviously). Before you are completely exhausted from the day. Or have his parents watch your baby and go out (or stay in). Or swap off once a week with another couple with a child so you have a date night every other week, and they get a date night opposite weeks.
About him talking to his parents, I'm going to guess that he tried to talk to you about it many times, and you couldn't hear You what he was saying. The truth is that when a person in a marriage says the same thing over and over and over and nothing changes, it is a big problem. You need to tend your marriage, and you and your dh neeed to figure out how to be acouple again as well as being parents.
May be tell him that next time, you want him to tell you that a problem is so serious that he is considering discussing it with his parents before he actually does. But considering that their advice is that he should do more around the house, I fail to see what you have to be angry about. They are supportive of your relationship. They tell him to be a good husband. What more could you want? And the path to avoid it in the future is to take his point of view and concerns seriously.
The worst advice on this thread is the advice that he should just get over it. That's kind of what your take was on it before, and that's why he went to his parents.