My son has just turned 8 months, but like you when he was 6 months I started thinking I should maybe do more stuff with him (only went to 2 or 3 baby groups before 6 months). However, I've still not done that much more with him :-)
At the mo, I take DS1 to nursery, come back with DS2, we play, I try to get him down for nap, then we go back to pick up DS1. We all have lunch, then DS2 goes for nap (hopefully!) in the afternoon and I play with DS1.
There are two baby groups on locally (I don't drive so can't get much further and I need to be back for DS1) and I hope to start going to them regularly, but to be honest, I actually quite like pottering round the house with DS2 and he's happy enough so I don't feel he's missing out that much, and that tends to make me lazy about going :-)
IMO babies don't really need baby groups and activities, they're just for the mums - if you're happy doing what you're doing just now, no worries, if you feel like you want to get out more, find out what's on locally, but don't kill yourself to do 'activities' every day unless you're the kind of person who needs that - I'm happy being lazy 