Your body is probably making up for the nausea hon (could also be bloating or fluid retention).

Please try not to worry (I know, easier said than done!). My fertility specialist explained it as your body preparing itself for a possible famine, like it would have done thousands of years ago e.g. storing up energy so that if you couldn't get to food, you'd have reserves (as baby takes what it needs to).

For what it's worth, I put on almost 10 kg (!) in the first tri as food was the only thing that helped my nausea. It slowed after that and seems to have plateaued now at about 15-16 kg total over the pregnancy. Sure, I have days where I feel heavy but I try to keep telling myself that my body is doing exactly what it needs to to be strong for labour and a healthy bub.

Hope you feel better about it soon and more importantly, congratulations!