Sonogram question

Stephanie • Princess, Wife & Mommy.

I went in for a sonogram and my hcg levels went from almost 2,500 to almost 21,000. The first sonogram done on Friday showed nothing and with the 21,000 result showed a gestational sac and yolk sac. They said they think I’m 4-5 weeks. Has anyone ever heard of twins developing at this point? I go back for another sonogram Friday