Hi M.,
You've made me realize how incredibly lucky I am to have the support line I do. We had our son on Thanksgiving and I am now 40 years old and WHOA! did I forget what the first months were like. I also have a 7 year old from my first marriage that is having some trouble bonding with his new brother but I too get isolated and feel overwhelmed. You feel trapped at home and are constantly trying to connect with some adult to get a connection back to adult life.
I have been on Zoloft for over 7 years, this started when I took on my ex husband and his two teenagers - they came as a package full time. I was still overwhelmed and ate to "get away", got up to 267 pounds too. Left him when my first son was 1, gastric bypass, lost 100 plus the 180 pounds of bad husband but there are still many times when I get down and sometimes don't understand why.
My suggestion would be to speak to your husband, ask him to have a sit down talk with the other kids, ask them to either help out more or to be aware of their bickering because it elevates your stress level just hearing them. Take the baby out for walks to your local Starbucks or coffee house - lots of people will want to see your baby and start conversations (I do this once a week to get away from the house) and some mom's are doing the same thing, you may meet someone there with a situation similar to yours. Humans, by nature, are empathetic and nosey...so offer another mom and baby to share your table or chat back and forth and try to meet again the same day next week. Soon you will have a couple of other friends and usually they have friends they introduce you to, etc.
It's tougher in the Winter because people don't like to go out much when it's colder but once you become a regular, even the employees will start to know you and your baby, most of the women like to see your baby grow and change.
You didn't mention where you live but I am in Alameda, laid off since last June and home with the little guy every day, so if you'd like to connect, email me and we can meet up. Depression, even slight, isn't a thing to mess with, you need to feel great so your baby and family thrive, you are the "glue".
I sincerely wish you the best and mine is only one suggestion but it helps me feel better - plus I get my mocha fix...good luck.
T