Someone help... Hcg levels

I should be about 5 weeks or almost 5 weeks. Last week my hcg was 305, about 56 hits later they didn't double but was 557. My dr wasn't worried but online has me scared to death. The next day I was in urgent care for chest pain and they checked my hcg levels and it was 746 and that was 28 hours later but still less than half of the double if you find the medium between 557 and double that which is like 1114. So far it's been going up about 80% just not a full double like I would like. Urgent care also gave me ultrasounds and saw no gestational sac but he said typically they don't see that untill at least 1000 hcg or so. Someone please just ease my worry Google is not my friend. Share stories and experiences please