I have a benign tumor on the lower right side of my head, is this why when I walk I feel like the ground is moving?

Possibly. Balance is largely regulated by mechanisms inside the ear and nerves that connect to these structures. If a tumor impinged on these structures, then balance could be disrupted, which might give the impression that the ground or other surroundings are moving. One common complaint is vertigo, which is frequently described as "the room is spinning".
Balance propriocept. Balance and proprioception may be affected, discuss with your neurosurgeon and treatment may be indicated.