BFP line progression???

Melissa

So we got our positive on Friday with a first response pregnancy test I took another one on Sunday and Monday with a dollar tree cheapy. Not seeing a huge difference in the lines doesn't seem to be getting much darker if any??? So I'm confused had a miscarriage back in December. We do have a healthy two-year-old so my doctor said we shouldn't be worried about this one but of course I'm worried...