Hello Lost. Is DS your first?
Having a baby is completely overwhelming for both body and mind. At only 3 weeks old it's completely normal for baby to want to feed a lot. You just need to park yourself on the sofa with food, drink, mobile and tv remote and give in to it.
Attempting to do anything more than maybe a short walk out can be like organising a military campaign. And exhausting.
Don't be too hard on yourself, this is really hard work, but it does pass. You need to find strategies to make life easy.
Can you pop your DS in a sling to get out or just to comfort him around the house? If you can pop him in a sling and grab your changing bag you'll be good to go.
Give up on housework and sleep when he sleeps if you can, or at least just lie down.
Get takeaway in, or get your DP to being in easy dinners from work, which he then cooks.
Have you tried swaddling? A dummy?
Hang in there, and ask for help from family, friends, HV.