New motherhood can definitely feel redundant and isolating. Baby's needs are pretty simple at this stage but they are *constant,* and it's a huge adjustment to have someone so completely and totally reliant on you for everything they need. Plus your body is weird, your hormones are weird, stuff is still leaking out of place, and you're so tired and distracted you often forget your own basic needs (sleep, food, shower, adult interaction, etc). Being a new mommy is hard, especially when you don't have much help.
1) Ask for more from your fiance. Nay, EXPECT it. He can stick baby in a Moby wrap or something while he plays a video game and you go wash your hair, or he can pause the game to take baby for a walk while you grab a catnap.
2) Ask for help from others. If you've been turning down help from grandma because you feel like she's your child and your responsibility, stop! It's OKAY to ask for help. It used to be normal for extended families to live together and for everyone to help with housework and childrearing, plus in the US it also used to be normal for families middle-class and above to employ household servants. Running a household and raising kids was NEVER meant to be a one person job, so if help is offered, take it!
3) Get out of the house. If there's some kind of early parenting group in your area that can be great, or your hospital might have classes or seminars especially for new parents. Or heck, just go grab a Starbucks and be around *people.* Even if you're not talking to anyone, just being around other people can boost the spirits. And who knows, maybe you'll meet some new mommy friends to trade war stories with. Anything is better than just sitting at home feeling lonely all day.