1 account splited on one world

So me and my friends have a world in minecraft, and I am the creater of the world. when I load in I get stuff and the n we stop playing, a little later we get back on and then all of a suddon I have nothing in my inventory, so I leave again and surely there, I have my stuff again, so I keep playing and then eventually log off, then I get back on and boom, Im back to my other self with nothing, I am playing on the same account but its like I have split people (2) that will randomly be selected to play as. lmk if you need more info