RawTherapee is kinda good, but also a mite frustrating if you've ever used Lightroom, which you've said you have. It's also mildly irritating that you've just graduated, since you could have used the student deal they have. GIMP also has a few reasonable photo editing features, which you could make use of.
What you can
do is download the Lightroom 5 Beta
, which will still be operational for a while longer, it expires on June 30, so you've got about two months.