my baby can't sleep and crying at night

[heinzzz]

my 18 month old baby is sharing bedroom with her 5 year old sister..normally she'd wake up like 2 times at night and i could calm her but the problem seem to be worsen last night. she woke up crying at 12.30am. Then at 2.05am, 3.45am, 5am, 6.15am, 6.30am, 7am. GOSH!!