What Causes Stomach Bloating And Cramping With Trousers/jeans?

hi i am 32 years old, 5ft 4in. when i sit down with trousers/jeans on and the waist band is obviously round my belly my stomach bloats up and have really bad cramps, i look around 7 months pregnant and this is so true. i do pass wind when this happens and it does relieve the pain a little, what causing this. thank you