I am having a similar situation since I stopped cocaine - I just cant be bothered to socialise with people unless I'm forced to.
I have made myself leave the house to see people but its very difficult to motivate myself. Once I am out with people I feel better and it really helps me.
I agree with "Inparticular" - take up a new hobby/interest. Last Monday I started back at the gym and am using my mountain bike on a daily basis. There a lots of free museums to visit in London, so I am going to try and visit one each week for the next few months.
The more I force myself to get out of the house the easier it becomes, although this is not the case every day.
It's good that you are taking your son fishing, I bet he really enjoys that
Are there any other activities you can take your son too, maybe this could be an opportunity to make new friends?