I don't know if this will help you, but many many men do not want to have sex while their wife is pregnant. My husband was like this with our first pregnancy. It had nothing to do with weight gain. In fact, it began when we had the 20 week ultrasound and he saw the baby looking like a real baby! From that point on, it was just odd to him to try and have sex with me while his son was in my uterus! He was also afraid of hurting me and the baby. After seeing me go through completely natural, med free labor, I think he was convinced that he would not hurt me, so with our second pregnancy things changed! it was just unchartered territory before.
Perhaps you can have a calm talk with him and tell him how you are feeling. Men are affected by pregnancy too. And if y'all are newlyweds AND pregnant, he may be feeling a lot of pressure as provider. This is something that strongly affects men. When I became a SAHM, my husband was very stressed in the role of sole provider. It took a few months for him to adjust. This could be an issue for your husband, too. Even if he isn't sole provider, he will soon be provider for a wife AND baby. Men are profoundly affected by changes in their lives like this. Talk to him and see if this is your issue.
****ETA Please please do not take to heart what the man below said. You are not an awful, pregnant, mean, unloving woman right now! Don't worry about being the "good little girl" - that is demeaning and not your problem at all. I hate that he popped on here to tell poor pregnant you that! So sorry you had to read that. Do not think your "moods" have turned your husband off of sex. I'm sure, like all the women here have said, that it is just scary for him how life is changing and hurting you and what not. It is not your hormones and moods that are turning him off, honey. IGNORE the man!
***ETA again, I guess the man took his response off. So ignore the rest of what i said! Maybe he realized he was wrong.