Only a weak BFP after HCG?

[TTC First]

I know they say that HCG can last up to 14 days in your system. I had my shot 48 hours ago and I haven't Oed so I did a pg test to see if it would pick uo the HCG. I was expecting a strong positive. I did a test but got a very weak positive less than 48 hours after the shot.

Anyone know if I should be seeing a strong positive? Maybe this is why I haven't Oed.