Can't stay logged in for more than 30s..

[SquarBoi]

Hi, I am experiencing an issue, don't know the reason for that, every time I login I either can't move, keep jumping back to where I was, or fall through the ground.. I can mine stuff when I can move, but they don't drop anything.. When I logoff and get back in, the items are then on the ground, but I can't pick them.. Please let me know what is happening..