Hello everyone, in March there will be 7 months but my belly is not bi…

Hello everyone, in March there will be 7 months but my belly is not big at all, there are ruptures, strong pains, my tummy looks like it's 4 months pregnant. I am 19 years old, height is 165 cm and weight has always been thin, somewhere around 52 kg. Now I weigh 57-58 and I'm gaining weight. My hips are not wide, I'm really worried about this, does this happen often?