I dont understand the impact of the HCG injection. Maybe you metabolised it faster or something.

It may also be faint because you pee'd throughout the night. If it were me, I'd be writing a date on the test and saving it to compare to tomorrow's test.... But I am a POAS addict. If the lines get fainter you could put it down to the injection working it's way out (understanding that all tests are different and shouldnt be compared etc).

Fingers & toes firmly crossed