Thanks for posting your query.
Menstrual periods have two phase: 1st day of menses up to ovulation is called as estrogen
phase and from ovulation up to the start of next menses is called as progesterone
When you got periods on 21 Dec
then on 26th Dec, you were in estrogen phase and physiologically uterine mucosa was not well prepared for conceiving.
So with this logic, there is no chance of pregnancy
and your urine pregnancy test is also negative.
You should consult with gynecologist and should go for thorough check up.
Although there is no chance, still you should go for ultrasound
imaging pelvis; there may be other pathology causing bleeding in spite of pregnancy.
Dr. Mayank Bhargava