First of all congratulations and well done to you. Three weeks is quite early to try and establish and routine, just keep him with you and feed him when he wants, easy to say hard to. Can you put him up in your room and use a baby monitor when you are downstairs? Might make you feel like you are having a bit of a break.
The first few weeks are a slog, so just keep your head down and get on with it, feed/sleep/poo is the basic gist for a while.
It sounds like things are off to a good start already, just try and relax as much as possible about it, just take it easy and not overthink stuff.
Even a walk round the block is worth it just to get out, have you post natal classess started yet? Have you joined a local National Childbirth Trust? Please do these things and meet others, get on the phone and invite them over for a coffee, it's like dating you will find people you click with and can share all the things about babies. It does not help with the weather being so cold. I listened to the radio a lot, Radio 4 (good plays and stuff, sounds odd but I was bizzarly really captivated about a documentary about corn farming in the USA) and Radio 5 to keep in touch with what was going on in the outside and Heart etc for music which helps lift spirits and CLassic FM for something relaxing.
So keep going, relax and have a chat with your health visitor, give them a call and they will come round, they are there to help.