Being left in the dust at work?

I have worked for a warehouse company for over 6 months now. The boss has 4 people that have worked for him no more than 3 months and a girl that has been there 19 months. Throughout the day people can either get items from the warehouse from a stack of papers with the customers name and place it in an aisle for a worker to deliver the next day, they can also put chairs together with screws and bolts, unload trucks of furniture or get rid of trash with a compacter, break down cardboard and sweep the warehouse. I tried to emble the charis one day without anyone telling me how to do it and I don't feel they were put together like they should and he never asked me to work in that area again. I pulled items from what is listed on the paper and I did it for a while and now he will say he doesn't want me to do this anymore. So basically everyday I clean up and do the trash and may unload a truck when it arrives. The boss never pointed out any mistakes to me. Sometimes he will tell me to sweep the warehouse even when it has been done several times already that day. I don't communicate much with the boss and come across as being shy. I sometimes feel he underestimates me and doesn't know for sure who is making the mistakes. I won't to be productive but it seems like I am not allowed to do what everyone else is doing. I feel I am being used and taken advantage of and don't feel like continuing to work for him. The boss must want to keep me though or he would have got rid of more before 6 months of employment. Is this situation berzerk and what gives here?