Slow raising hcg levels

So I went into my doctors office for blood work on April 2, my period was suppose to start April 1st but didn’t come to April 3rd. So I got the results back and my levels were 9. So I went back April 5th for more blood work and the levels was 13. So he insists I go back on April 9th where my levels went up to 33. So at this point I’m confused as to why my levels are slowly raising and how if I had a period at the beginning of the month. So April 10th I did 4 pregnancy test which all came back positive (Yayyy) so still confused I go to the ER on April 11th. They did blood work and ultrasound which hcg levels were 66 and nothing can be seen on the ultrasound but fibroids which is outside of my uterus. So I go back to my doctor on April 24th where I did more blood work and the levels were 118. So I go back to the er yesterday April 27th and my levels are now 146. I have to follow up at the er for more blood work tomorrow. Can anyone help me with this or has this happen to anyone?