I had a similar "rebound" after bil died -kind of an emptiness - but it was a bit different for us because we finally got to go back home and get into our normal routine again.
So for you being and living so close to him like you did, it is probably a lot harder to make the adjustment or change back to "normal".
Plus you did it for a lot longer - we were only gone for 2 weeks total.

Time will help too, maybe at some point you might feel like signing up for a class or activity to help get you back into a routine and meeting new people again.