Could it be twins?

Hi ladies,

It's my first pregnancy and I'm somewhat in the dark, so please bear with me. I'm currently in week 9 of my pregnancy and am already really swollen. Everything that I've read tells me that it can't be a bump but it just doesn't feel like gas. My hcg levels were really high from the outset which meant I discovered the pregnancy very early on. I had an early scan at 6 weeks and they found the heart beat for one baby (yay) but also an empty gestational sac. I am going back for another scan in a couple of weeks as they think it could be disappearing twin syndrome but my appetite is through the roof, boobs are huge and belly is getting big. Is there any way the second baby could just be slower to develop?

Sorry if that's a really stupid question! M x