Does anybody know what is going on with me?

Hi Everybody,
It has been a while but to be as brief as possible, I suffer from severe SAD which I basically self diangnosed early last year and have been on medication and light therapy and last year was the best year I have had in probably 20 years. Well, anyway, at the beginning of this year I started feeling bad again, purchased replacement lights for my lightbox which seemed to do the trick until I think this past April. Anyway, at that time, I started taking Melatonin because I just was never sleepy and felt it would eventually catch up with me. Before I started taking the melatonin, I felt really good. I wasn't depressed at all, just was never tired. Since taking the melatonin, it seems that that is when I started feeling bad again - mind you, I have been off of the melatonin for many months and still feel bad and it is summer. I cannot say that I feel depressed. I just am tired. Because of this, it has affected my work and I got put on an improvement plan and I have been trying and trying but I still feel so tired during the daytime. The only time I feel good is when I am in bed and it seems that is when I start waking up which is not good because then I am tired all day at work. I do not know what to do. Does anyone have any ideas?