How do i know there is a ghost in my room?

Hey my name is Amanda i'm 16 i've been ryly interestead in da paranormal world i haven't done reasearch on it in bout 4months but eva since i've had a few paranormal stuff happen...encounter1 my mom was downstairs n every1 was in dere room n she saw a white figure walk across da livin room upstairs, encounter2 i changed da furniture in my room 2days l8er i was awake n my dad was downstairs n sis was in the kitchen n i heard somefin whisper in my ear i turned round n no1 was dere den i heard a buzz n nofin was in my room encounter3 i was home alone 2daii 8/1/09 n i had my music on really loudly and i went to the kitchen to get water i was listenin to lilly allen smile and i herd some1 callin my name 4 times n it sounded exactly lyk white noise lyk it was comeing from the speakers i started shaking n cryin out of nowere(*note* i played the song again n i stayed in my room n i didnt hear it again)...i get chills here n there in my house and my grandfathers ashes are downstairs i dnt think it is him but it can b a posibility i jus want to know how i know there is a ghost an itz not "all in my head" lyk my father told me also my dog stares at places as thoough some1 is there and there isnt anyone n also if i'm home alone and i am sittin downstairs i hear ppl walkin round upstairs (*note* itz a reversed raised ranch house 2 floors 3bedrooms upstairs with livin room 2 baths n kitchen n downstairs garage bedroom bathroom n livin room) if any one can help please i would really appreciate it!!!! and thnx