How to get my hours cut at work?

I'm due oct 15th and starting sept I would like my hours cut. I'm in the military and had them cut last year (4 hour shifts) but that's cuz my supervisor was cool af. Now I have a different supervisor and she's pretty strict. Of course I'd need a doctor's note which is fine cuz my dr said she'd write one but I think I need a medical reason for my hours to get cut. Honestly this is my second pregnancy and I have no medical problems thankfully but I'm just exhausted and very very uncomfortable. I'm bigger than my first pregnancy and I'm swollen which didn't happen with my first. I don't even know how I still fit into my combat boots but it won't be long before I can't. Any advice on what my excuse could be to cut my hours?