5 months post acl pains

Hello there. I had my acl reconstruction in Janurary 2010. I was given a hamstring graft and went to physical therapy the first two months. The third month I only went so often and by the fourth month I just stop going because of classes and a new job I started(where I carry a lot of equipment). The past month I have been on on a trip for work and school and I have stop doing my exercises. since then I have been experiencing pains in the knee. Most of the time it is when I am sitting down and after I have been standing up for long periods of time. I was wondering if it is okay to be having pains this far along after surgery. Also is it too late to help it go away and start physical therapy again. I was told I would be able to return to sports after 6 months but now I think I might not be able too for much longer. I really slacked off these past three months but I am willing to work as hard as possible to regain strength. I dont think I retore the graft but I do think my muscles are weak again and maybe it has been slightly damaged. Is it too late???