Could you do one on one talk therapy? Maybe online and you can stay with LO.
Don’t put too much pressure on yourself. It’s still early days - give it time. Keep talking and try things in small ways
I feel you because I felt the same. Firstly, be kind to yourself, you're still in the early days of post-partum. Even with the easiest and smoothest birth, your body and mind are still adapting and changing so it can be rough. Speak to your GP, see if there is anything they can do. They may refer you for therapy, I'm in the UK and used Talking Therapies and they were fantastic. If therapy sounds too much right now maybe start with some self-help/care books. 'Raising a Good Mother' is a fantastic book to start with and even gives you Journal prompts etc. Read it and you'll see that you are 1000% not alone. It sounds like you're having a tough time with LO and sounds like he's having a tough time. However, it's important you look after yourself so that you may provide the best care for him.
I understand your fears, I was the same and isolated myself. In hindsight though, it's not healthy or sustainable. You need the support from others. Especially if your poor little boy is struggling. Start with just having a coffee with someone, meet in public if that's more comfortable than at home. Then, if you trust partners mum then ask her to watch baby just while you go in another room to bath or nap or read, start small, just 15 minutes or an hour, whatever you're comfortable with. Build up from here. It'll get easier but it's also understandable to find it hard to leave baby at the start so be kind to yourself. It takes time and there's no rush. Sorry for the long messages but I just feel your struggle and I do understand. You've got this mama. You're gonna be OK and so is your little boy. Everything is temporary. This feeling will pass and this newborn stage will be a memory before long and not a battlefield you're currently in.
Straterra is an SNRI, it may help? Serotonin is predominantly made in the gut. If you've been on antibiotics within 6-12months it's been shown to increase depression and anxiety, due to poor gut health. You may also get tested for h. Pylori. I'm in the process of getting tested as my nephew had it for years and was on an adult dosage of protonixs until a new doctor tested for it approx. 3yr later. I understand brocoli sprouts kill h. Pylori.