It is unlikely that you are pregnant.
I presume that you did not have intercourse after 12th December. If you had recent intercourse, then pregnancy
cannot be excluded.
Best thing is get a pregnancy test done with serum or urine.
Negative result does not exclude pregnancy completely but only reveals that pregnancy is not of that duration which can be detected by that test.
If you did not have contact after 12th Dec. and if the pregnancy test is negative, then you are not pregnant 100 %.