If you want to cheer up after reading Mockingjay, then I highly recommend The Road. It is one of the most touching father-son relationships I have read, as a father and his young son trek down a road in post-apocalyptic America. The landscape is cold and barren, the few people they come across dehumanized and brutal, but the father keeps his son going as they move South, carry the flame, and look for the good guys.