Stay at home is making me crazy :)

So the baby is now 2 months old and my little monkey is going to start school when summer is over. My darling baby daddy is now working the graveyard shift and so I am a stay at home mom. At first I loved it - spend all day with the kids, don't have to have any of the stress of working. However after a couple of weeks of this stuff there are a few things that I have noticed:

1. With all of us home all the time the house never stays clean for even a day.
2. We live in the south so the average summer temp is about 100 - too hot to take the kids to the park (esp. the 2 month old) so our activities are limited

The walls seem to be slowing closing in on me and Im starting to run out of ideas to keep a 5 yo entertained for a majority of the day - I even googled stay at home mom. How do you keep from going crazy and what is it I do all day.