He sounds immature. How old are you both?
The human body changes in wonderful ways when undergoing the process of creating a new life. Sex while pregnant is possible. It really won't hurt the baby (unless it's on the way out at the time!
Yes, you're a bit larger than you used to be. That's the wonderment of bringing a new life into the world. My GF has stretch marks and I'm proud of them (though they're not mine). It's a sign that she has had a full life, bring babies into the world. It's a badge of honor.
When your husband makes fun of you, just tell him that he married "the fat girl"! (you know you will gain weight and that you will lose it later.) Joke back with him. Ask him how he likes making love to a beach ball?
As for sex during pregnancy -- at 8 months, go easy...but one technique my (ex)wife and I used was to have her on her back, legs spread. He lays perpendicular to her on his side. She can put one leg over his lower leg, the other under his chest. He enters making a human cross (or X pattern) and proceeds to give you pleasure. There's no pressure on your stomach and you need only concentrate on the feelings.
The human body changes in wondrous ways over the course of a lifetime. Stretch marks, crows feet, laugh lines, a few pounds in middle age, skin & bones in old age...it's all good, girl. Be proud of your body! Tell him if he wants to know what to look forward to to visit your grandmother. And to ask her how she enjoyed life!