Things will get easier for you when your son goes to school! You'll have those extra hrs to work or train plus more time for you, relationships etc. Keep holding into that because as he gets older, he'll grow out of this toddler stage and become a close, loving boy.
My son drove me mad when he was under 5, really hard work. But now at nearly 10, he's far easier and more cuddly than my girls who just bicker with each other. It won't stay like this forever for you, it will improve. You are surviving each day! Keep pushing through!
The early years are like a fog and overwhelming, especially for single parents and those without family support. Depression and anxiety are very hard to overcome. If you could perhaps ask your mum to take your DS for a few more hrs or be there in the house with you both for support, things may feel better. I understand what you mean about children not being still in shops but do try nonetheless.
My thoughts are with you. I suffer from BPD and comorbidity ( anxiety/ suicide ideation) - diagnosed in my late 20's and fight my condition every day along with far too many health problems! Try your best to keep strong and know that it will be worth it all to see our children grown up and happy.
Don't give up. I too used to take my children to the cafes and sit there for a while with them , then go to the park. It's become such a usual thing for me to do that I still take them for coffee ( in their case hot choc or juice) once a week. It's become part of our routine! Trust me, getting out to the shops and cafés was a lifeline and kept me positive when I was struggling. Treat yourself to nice things; candles, baths, a good film or book.... Anything that helps. I'm not overly treatable via the NHS ( except CBT ) and I'm a closed shop to counseling but I help myself instead; self help books, videos, articles etc that discuss BPD and how to cope. Unserstanding my diagnosis helps me control it.
Maybe try holistic healing as well as your mental health team. Yoga,reiki, crystals, wholesome foods, green tea, meditation etc. This, as well as my faith helps me stabilize a bit and keeps me calmer.
You can do this and you are not alone - it will get better! Sending you brew and flowers ( icon on my iPhone won't work!)