Thanks for posting your query.
There are three possibilities-
Your second test kit is defective and has given a false negative result.
Second, you have undergone a missed abortion
and the third possibility, is that you have an ectopic pregnancy
which at times can rupture and can cause life threatening complications.
You should consult a gynecologist at the earliest for physical examination and get serum beta hCG
levels which are more specific and sensitive and get an ultrasound
I will be available for your follow up queries.