Congrats! I remember when I first stayed home. It was a huge change, even though I wanted to do it wholeheartedly! In my case, I didn't realize how much of my identity was wrapped up in my job. I didn't know who I was without it. Here's some ideas to get you out of your rut.
Can your husband give you some time away from the house to get together with friends?
Have you had anyone over to visit?
Do you have family or friends you could leave your son with for 1-2 hours so you can grab a bite to eat with your husband, even if it means fast food?
Does your pediatrician also say you can't go to church? That was a big one for me.
Is your son's immune system really that weak, or is your pediatrician that conservative? Docs used to make women stay home for 8 wks after they were born, regardless of the baby's health. If you're breastfeeding and he hasn't had a lot of problems with being sick, he should be getting a stronger immune system by now, although it will not be "full strength" for quite some time (breastmilk helps a lot there). If he's been healthy since coming home from NICU, I'd look for a different pediatrician.
We had a daughter born 3 weeks early with severe genetic abnormalities. She was in NICU for 2 1/2 weeks. She received breastmilk through a stomach tube. While 3 weeks is different from 6 weeks premature, she was at high risk for "catching" things. Not once did our pediatrician recommend we keep her at home. We didn't do a lot with her out of the home, because it was difficult to get out. But we did get out some. Friends visiting and a getting out a couple of times to meet friends for lunch helped a lot.
Enjoy your blessing!