What Causes Irregularities In Menstruation?

Hello doctor....I had my last period on 1st July....and then after trying for baby...I am experiencing continuous pain in my stomach from last 10 days.my cycle is normally of 28 days and I have not yet had my periods.i did a prega sure home test today morning and it wAs negative.this is my first month of trying for baby.is there still a chance I can be expecting