That does sound like a kind of depression. A sort of base line flatness or low mood. There can still be moments of happiness but the base line isn't neutral or content, it's heavy.
There are things you can try to do to lift it.
Strenuous exercise 3 times a week for at least 45 minutes is a good mood booster.
Being out in nature. Even just sitting in a park or by water. Or just opening a window and gazing at the sky or the trees.
Certain foods boost serotonin - walnuts, almonds and other nuts and seeds, blue cheese and other dairy products esp cheese and yoghurt, grapefruit, eggs, salmon and other oily fish, turkey and other lean meats. You could try having at least one or two of these at each meal.
Also try supplements for Vit B complex, Vit D (if you are in a very hot or very cold country you might not be outdoors often enough to process Vitamin D from the sun. Iron too, but use a plant based one so it doesn't cause constipation.
I once had anhedonia - the kind of depression where nothing brings you joy. It's very scary. I cured it by trying something new everyday for a year, Do something you have never done before and keep a record of your reaction to it. A new fruit or veg, a new type of music, new soap scent, new route home from somewhere you often go. You don't have to enjoy any of them, but do keep a record of them, as that makes you pay attention. Also, when you loook back through the diary or private blog, you will see progress, and realise your life has improved.
Bit by bit, increase the effort the new things require - go to a talk, an evening class, a creative workshop. If childcare etc keep you house bound, try online free uni courses, workouts, dance routines. Say yes to things you usually make excuses about. No need to commit to anything more than once but if you enjoy things or they spark interest, keep at them. Pursue those new avenues. I read somewhere that doing new things creates new neural pathways in the brain, and that these can prevent you from looping back to the same low mood (it was ages ago. I forget the science now. But you could look it up.) It was a very fun thing to do, anyway, and made a massive difference at the time.
Another thing that might help is to divide life into 9 equal parts - family, relationship, friends, personal development, fitness and health, spiritual life, community contribution etc. Then do something every week to enhance this aspect of your life. Might be baking or reading with your DC if you don't usually, a date night with your partner etc. The nine aspects can be anything you like, but you are encouraged ot include community contribution as that helps you feel like you belong. That could be helping at school, political or religious group, local charity or community project. Not sure if this will help if you are feeling so flat, but you could combine it with the new things project and see if together they make a difference.