Hi, My Sisters Stomach Has Been Growing.. She Looks Pregnant,

hi, my sisters stomach has been growing.. she looks pregnant, she missed her period.. her last period was in janurary and it was only spotting and she says shes been feeling movement in her stomach and the doctors couldn't find anything wrong with her.. pregnancy tests were neg and shes already been checked for cancer or any other diseases but they didn't find anything wrong with her they have no idea why she looks pregnant.. she looks about 6 or 7 months pregnant.