How To Treat Pigmentation On The Abdominal Area?

Hi, I am 21 and male and have had eczema since birth. The problem I am having is with pigmentation on my abdominal area. The skin on my stomach is darker than the rest of my skin and LOOKS dirty however it is not dirt and seems to be in the skin. I have had this problem for over a year now and it varies in degrees of severity. The skin also sometimes looks like it has a shiny film over it. My skin does get very dry at times and this has lead me to wonder if the discolouration is due to a build up of dead dry skin cells, I have tried exfoliation but my eczema does not respond well to this. Also I have tried keeping the area well moisturised using diprobase and eucerin (containing urea) which helps to reduce the appearance after application but always comes back. I also thought this problem might be really mild stretch marks but dont know if this is likely?? I am really confused by this problem and would appreciate your expertise. Thanks