What Causes Delayed Withdrawal Bleeding After Taking Microgynon?

Hi, I take microgynon 30 and have stuck to the 21 pills on time and then the 7 day break and I had a withdrawal bleed from my last break but I started the next strip 2days late (wednesday when it should have been monday). I left the missed pills (monday & tuesdays) and took the pill I was due to take on the day (wednesdays) and then took all the rest of the pills on time. I also took one pill extra after my 3weeks of pills so I had a pill on monday when I should've started my 7day break. I did not have unprotected sex in the 1st week of my new strip but I did in the last week of that strip. It's now thursday and I have still not had a withdrawal bleed and I'm getting worried. Could I be pregnant? And when will a pregnancy test show an accurate result? I took a pregnancy test the 1st day of my 7day break and it showed negative but it had then only been 4/5days since I last had unprotected sex last week thursday and friday. PLEASE help!!