I understand your concern. During pregnancy there is a hormone produced known as the Human chronic gonadotropin (HCG), which is seen in blood and urine. This is produced immediately after fertilization of the egg and gradually increases and reaches optimum levels during 4- 6 week of pregnancy. There are two types of tests to determine pregnancy:
a) Urine tests: here since HCG is also seen in urine, a convenient method is known as Home pregnancy test can be done where the urine sample can detect the levels of HCG and confirm the pregnancy. However sometimes there is a small percentage of false negative where it is seen in three conditions:
a)You have tested 6-7 days after ovulation using a home kit. In such a case, the test appears negative, as there is not enough HCG in the urine.
b)Urine is diluted as the patient as had a lot of water, so the test appears negative.
c)Sensitivity of the test is low as seen in home kits.
The other available test is the blood test where HCG levels are measured in the blood and is more accurate than the urine test and can detect much earlier than the urine test. I would suggest you to get an ultrasound scan along with these reports and consult your obg-gyn doctor.