I'm on my own practically every day of the week including Sundays. I don't see a lot of family now, all busy and grandchildren doing their various activities too especially at weekends.
I know how you feel, however you do have lots of friends and family there for you in the week. I don't. Friends are either quite unwell, moved away or deceased, family are all at work in the week so don't see them often in the week either.
But I go for walks, often take the car off somewhere to walk in greenery. I love gardening and have a home to tend to, always something to see to. I enjoy [good] TV, read a lot, use the laptop, revive old pieces of furniture, actually enjoy shopping for food, cooking and new recipes. I've many interests.
It's ok, I like my own company, peace and quiet. I go with the weather a lot of the time. Sunday is no different to any other day for me really. Yesterday I went for an hour's walk in a local park, watched women's football on TV in the afternoon, pottered in the garden, new recipe for dinner, did some research on the computer, watched SUTC Bake Off and read more of a very good book. Boring for some but I was content.
I feel very lonely sometimes, but shake it off/keep my spirits up by reminding myself how free I am, how lucky to be in good health and able to indulge in my interests. Basically I accept that life has changed and go with it, there are innumerable things to do in life with our time and to fulfil us. We have to find resources within ourselves not depend on others.