HPT line not getting darker

mo
I'm sorry, I feel like I've posted so many times but I can't stop my racing mind.
Has anyone ever had lines on a FRER not get any darker and gone on to have a successful pregnancy? I've taken the test at 11, 12 and 13 DPO and they've been about the same level of darkness. Yesterday was a tiny bit lighter. 
I also had some strong cramping and a little brown discharge (which stopped) so I'm getting so worried that it's a chemical pregnancy. I've contacted my doctor to see if I can get a blood test for better measure but would appreciate input in the meanwhile!