What Causes Faint Positive Line In The Pregnancy Test Strip?

hello I have done ALOT of tests every single test has a very very faint positive but not getting darker. I have no bleeding no pain . I have abit of a belly and its very noticeable as im only size 8. went to doctor he checked my cervix and said I am pregnant and it has a blue tinge. but y arnt the tests getting darker??? am I pregnant. I also have another son who is two. emergency c section. I am not on pill either. I have had 3 miss carriage also. just want to see those bright lines.