Assuming that your last month period was on December 10th You had unprotected sex in the danger period (Dec.22nd to Dec.28th). You are having mild stomach and back cramps
with light brown discharge & sore tender breast. Pregnancy
can be tested only after 20th to 25th of this month, if you miss your period on Jan 10th. The rest of the complaints may be pre period or due to some other cause. Do necesory investigations including USG abdomen. Consult a gynecologist.