Our futon sinks/sags surrounded by the fund how do i hold it adjectives? its a wooden futon frame with a 2 piece mattress ....

its a wooden futon frame with a 2 piece mattress . it sags contained by the back and its humiliated. any ideas how to fix it?
Answers:    If its the steel framed varriety the two frames should be connected at two points within the back near brackets that go into 4 holes along the frames to hold on to it to gether. you may be missing them