My custom skin isn't showing, I've tried everything like re-installing Minecraft, checking the skin file, installing the newest version of java. Everything!

I'm pretty sure that my Minecraft isn't in offline mode or anything. My skin would only show up as Steve, I use my skin as a slim skin and it would only load up as a slim Steve. I don't know what the problem is. 

My skin showed up as Steve for months now because I got no clue how to fix this issue.