aq, My Dd goes to a swimming class each week. This way we are told what to do and so i dont have to come up with creative things to do in the water
She goes to a tumble tots type class at our local leisure centre. They have sports equipment and a bouncy castle. Lots of other mums there but they are all trying to keep their LOs in check so you only have to talk to people if you want to.
My library does a storytime session weekly. I dont go to it but i know some people thing they are great.
Before DD started preschool on Fridays I would always try and arrange playdates on fridays. She is used to having some kind of 'activity' ie, preschool, swim, friend in the mornings, and then chilling out/playing with toys/watching tv/in garden etc in the afternoons. I think the routine helps me too as i find it difficult to be creative with activities and there is only so much time they'll spend on jigsaws and toys etc at this age.
Try and get DS1 involved with helping you with DS2. My DD helps me get the nappies now (gets cross if i dont let her), took some (very lopsided) photos of DD2s first baby rice yesterday.
hth - its all very easy to say but when you are feeling low in yourself it is hard. Even more reason to find some structure imo