Reduced work hours 3rd trimester?

Hi all, how do I ask to reduce my working hours at work? I’m 30 weeks pregnant and get bad headaches and swelling because I sit all day and work in the Insurance industry. So I sit and talk to customers all day about their policies. My boss isn’t too mice either, he expects me to come back to work after 3 weeks when I give birth... and I just feel so emotional and mentally drained from working here right now... I want to reduce my hours until I go into labor but two employees are leaving on vacation for a month and I don’t know if he’ll let me just reduce my hours since those employees will be gone.. but I feel so horrible here.. I don’t even get a normal lunch. I have to work through my lunch by eating at my desk and if someone calls I have to pick up. There’s no HR here since he’s owner and it’s a small private firm... and I can’t really report him to anything because he’s a family friend. But that’s just how it is here at his office. So what can I do to get my work hours reduced?