Hcg levels

My period isn’t due until Tuesday but on Thursday I took a dollar tree test and it was very light positive. I took another test in the morning and I was def little darker but still faint. Called my doctor and she did bloods on Friday which was 15. She stated it’s very low but I am pregnant and will redo my bloods this Tuesday. Is level 15 a sign that something is up? I’m scared I have had a chemical pregnancy two years ago and my husband and I and everyone was happy but not with this levels idk what to think. Has anyone had this and it’s doubled within 4days?