Hi, and thanks for your medical question on eHealth forum!
If you were expecting your periods on 28th of Jan and have not had them still and have tested for the pregnancy and it is negative, then you are not testing early. Go for a blood pregnancy test as you are trying to conceive. At times HCG level is too low in the first few days. So a blood test done now should be bale to detect it. If this too is negative, then consult your gynecologist.
If it is not pregnancy then other causes of delayed periods like lifestyle changes, severe anemia, prolonged illness (may not be very prolonged but a course of antibiotic could have messed every thing up), STDs, hypothyroidism, adrenal gland problems, weight gain, weight loss, and PCOS have to be ruled out.
Some of these can cause difficulty in conceiving and need to be looked into seriously. Since a confirmed diagnosis cannot be given on net please discuss these possibilities with your gynecologist once. Hope this helps. Take care!