Chemical or faulty tests?

Last month at 11dpo I got an incredibly faint pink line on frer. The next day it was negative. This month, 11dpo, the exact same thing happened, also on frer. I am trying to figure out if this is just bad luck with these tests, or if I am now having monthly chemicals. My period arrived last month right on time, and it wasn't heavier than normal. I had a 18 week loss in May so maybe my body is still working on recovering. I am losing hope that I will ever get my rainbow baby that would finish our family. Any insight would be appreciated. xo