Chemical pregnancy?

I Am 4 weeks pregnant, I got my first positive a week ago a very clear positive and the next few days my lines got darker. They are now faint, even the cheap tests are taking forever to show the line. I’m 15 dpo. Is this normal. So far I’ve had no bleeding at all .... wouldn’t I be bleeding if I was having a chemical? Why did the lines go from so bold and dark to almost nothing? I still feel very pregnant and haven’t even spotted or anything.

I went to have blood drawn today but I won’t know anything until Thursday because I have to go back Wednesday to get the second blood draw done so they can see if they are doubling. I’m just going insane. :(