Working during pregnancy

I work 10 hours a day, 5 days a week. I am a server at a restaurant. I am on my feet all day, and some of my daily tasks include putting chairs up and down off of tables, taking carts of plates to the back and changing the buckets out. I’m 10 weeks and i have awful back pain. Working has been taking a toll on me. My boss shows no sympathy what so ever. He tells me that’s my personal life and not to bring it to work. Is there any way my doctor may write a note only allowing me to work so much? I feel like I’m overdoing it. I get awful cramping in my stomach towards the end of the day, and I’ve talked to my boss, and he just seems to not care.