hcg! help please!

Rebecca • May 30th 2013 received my first son! ttc baby #2 since September 2014.
My hcg was 15 on Saturday on Monday it had went up to 33 and today it was only 39! So it increased but didn't come close to doubling! I'm freaking out! Anyone have similar stories? I'm so afraid I'm going to lose this baby 😩😭