I know it's tough. I realized that over the years I had isolated myself. Unintentional. Life with kids does that and before you know it the phone stops ringing and the invites cease. You can't even pinpoint when it happened. It just does.
You sound like you're doing the right things though.
There is a web site called Meet Up. It's not what it sounds like. It is more for people looking to find other people with similar interests. There is something on there for everyone, whether it be a running group, or a walking group. You could try a book club or a film society. Something with a focus. It will also remind you that you are more than a mother and more than a wife. You are someone with opinions and ideas who matters.
If/when you are able to get a few days away then look into a group called FlashPack. I am planning a weekend canoeing in Scotland in May. I am still standing by my marriage but I am not going to stop living whilst I wait for him to sort his [censored] out.
Re the weight. That happens to most of us. It is the flight or fight response not having anywhere to go. We can't fight and we can't flee so the adrenalin has no-where to go. We are stuck. You can't eat when your body is on an adrenalin high. I lost 20% of my body weight in 2 weeks. I didn't even realise I had stopped eating. It gave me a good base to start my fitness kick from. I had to avoid cardio - I didn't have any weight left to lose, but focused instead on yoga and pilates. I have never been in better shape. Silver lining.