Baby measuring smaller

Suzanne • One ☀️ baby👧🏻2/14/17, one Angel 👼🏼Oct 2018, pregnant with our 🌈👶🏻 due 11/22/19. All conceived via IUI

Today I went in for a second scan. Last Thursday I measured 5w6days with no heartbeat, today measured 6w1day (although the computer said gestational age 6w3days) with a HEARTBEAT of 114. They said they like to see it over 100 so I met that, I go back in 1 week. Does anyone know what this could mean or has anyone had experience with this before???