IUI and chemical pregnancy

Ashley • 28 // married to my best friend January 2015 // ttc baby #1 with unexplained infertility
I just got the call from my doctor that I am having a chemical pregnancy. They told me my hcg levels are elevated at 16. At this point, 17 days past trigger shot, if it was a viable pregnancy they said it would be at at least 50. 😔 
Having mixed emotions now. Happy to know that our first IUI was partially successful and that the sperm fertilized my egg. But super sad that it didn't stick. 😔 
How common are chemical pregnancies? My dr. Said it could be hormone imbalance, or the lining of my uterus not being thick enough. Multiple things.