Alex - you have the 3 day blues. Honestly, day 3 is the absolute pits. Your milk is coming in, your body hormones are settling after birth and you are tired. Do whatever you need to do today to feel sane, hole up, don't feel obliged to see people and just survive it.
You will feel better tomorrow, I promise.
I remember trying to hold it all together on day3 with DS1 as they wanted to take him to nicu again and were giving me lots of headtilts at the amount of crying going on. DH would stand at the curtains and keep an eye out for the arrival of midwives to give me a moment to get my sh*t togtethe before they arrived!
With DS3 I stupidly made an appointment at the GP about the state of my bum on day3. I turned up late and dr refused to see me (no, I am not kidding - I was 10 mins late 3 days post birth - the git) and I sobbed. With snot. In the waiting room.
I went home, DH took one look at me, sighed and said "You know you can't be seen in public on day 3. What were you thinking going outside??!!".