Oh dear! Sadly unless someone has been through a loss themselves, I don't think they have any idea how terribly hard it is to learn to live with it. Honestly, four weeks is nothing. I know the feeling of not wanting to get out of bed because you have nothing to get up for, but for your own health and because your lost loved one would not want you to make yourself unwell, you should at least try to make sure you eat and drink enough each day. That is hard, because you have no appetite and don't notice time passing when you are feeling so low, but please try. It will only make things worse if you make yourself ill also, as you have already discovered.
I know it feels like the world has ended and it's hard to understand how others can still act as though everything has gone back to normal, when for you, it never will, but that is one of the things about loss. The 'normal' that you knew won't come back and neither will the old you, but that doesn't mean your life is over. It really doesn't. What it means is that you slowly have to adjust to the new 'normal' that you find yourself in and to the new you this terrible experience has made of you. Slowly, you do find your way forward, but in my experience, you have to look for that, a little bit at a time. You need to find things that help you, in however small a way, to feel better, even if it is just having some flowers around so that you have something pretty to look at and a lovely scent to smell. For me, they reminded me that there are still good things in the world. Similarly, it helped me to go out and walk, partly to get me out of the house and partly because, if you have a park or open space somewhere near you, I found it helped to go and sit there to try to grasp what had happened and absorb it. The park was a lovely calming place to sit and do that in with all the greenery around and the sunshine to enjoy. It helped me too to see all the benches with their lovely inscriptions to loved ones others had lost but still remembered and missed and loved. It helped me remember that love never dies and those we love remain part of us for as long as we live and so never really leave us.
In time, it may help you to take up a new interest and make some new friends to give you something to look forward to each week and a reason to go out, but for now, how about starting a journal or perhaps a memory book. It helped me to make a photo album of favourite pictures of the person I had lost so I could look at them whenever I needed to, but it also helped to write down each day how i was feeling and what I was thinking about and that helped me get it out of my system a bit. Also you could start a book of memories, to help you look beyond the last days of your husband's life and remember all the good times you spent together. Revisiting some of the places you used to go to together might help with this also.
Grief should not just be about the misery and the sadness of that person not being there, but also about being thankful for the privilege of having known them and for the gift of the time you had with them. The memory of those will be the treasure you take with you into your future - and you do have a future. You just have to make it now for yourself, as he is not there to help make you happy himself anymore. So try to do that for him and that way, when you meet again, you can tell him about all the things you did after he was gone and make him proud of you for finding a way forward and making the most of your life after your time together, which, as someone who loved you, I am sure he would want.
One day at a time for now and even getting up and making a cup of tea or a meal is a little triumph and a start towards recovery. Sending strength.