Help , Whats wrong with my mare????

ok so iv had a mare for almost a year now , up until now shes been fine , but she wont lie down or sleep , as i stayed with her for the past few nights , she keeps looking at her tummy , I'm very worried about her , she is Arabian ,Grey and 16.2 hands shes 8 yrs old as well , her last owner kept her in a Field with mares and geldings and a stallion once as she has all ready when he had her had a filly .