Why do my Co-workers think I'm Lazy? PLEASE HELP!!!?

Basically the situation falls like this. Last May I was recently chosen to be a manager for a retail company. I am the youngest manager in my district and still am today. At work I am responsible for a lot of typical retail tasks like cleaning things up, setting up new planograms, etc... Typically at work, we are required to work 50 hours a week. I always work the full amount of hours and not only that but I stay extra to help when the stores need me. I do a lot of the little things like help other people out when they need help and I do a lot of the tasks myself which I could delegate out to other people easily. Being new in the management role I don't give a lot of credit to myself because I always give it to the team. I still do make mistakes because I am new to this career path but I never make the same mistake twice. The store has 2 other manager in the stores and 1 store manager. I can safely say that out of the other 3 managers there is only one other manager there that does his work himself with a mix of delegating. The other 2 managers including the store manager just delegate all the time and push their work on everyone else. The problem is one of my employees (Not a manager) came up to me and told me truthfully that almost everyone (including the other managers) perceived me as not doing anything and he reassured me that he did not think that and he was angry that the other employees did so he stood up to them. He is basically a hard worker like me that doesn't brag about anything but gets his job done. The problem is when the other managers are not present, I do a lot of their work for them and I volunteer to do as much as I can even if my plate is full. I also do tasks such as cleaning the toilets, ringing at the registers, etc. when all the other managers are complaining about even doing that. My store manager recently gave me a review and he marked me high on the work ethic part and said I was one of the hardest working manager there especially during the holidays. Why are other people trashing me and how come the other managers are? What can I do to prove that I am not lazy? Please help!