A lot of weight gain/ retained water

How do you know if the weight gain is retained water or actual fat? Prior to being pregnant I weighed about 135/140 and was actually very skinny, over months I’ve gained a lot of weight very quickly, my legs are much bigger, as well as my face and my arms have some extra weight on them compared to before. I weigh about 193/198lbs currently. I’m curious about other people’s experiences with this kinda stuff? Did you lose weight quickly? Was it water or actual fat?