period more than 2 weeks late one test positive followed by two negatives

Hi everyone, my story goes like this. I was on the pill for 1yeal\r and a half. Took my last one on 8July had a normal period, the next one came on 18August, thats 2weeks late. Now i have not had a period since then. Sice my period was usually on a 30day basis (before going on the pill) i took a test when i was a few days late and came back negative. Then 2 weeks later (on sunday) i done one came out positive and did another 2 on monday to see if it was true but came out negative. Still no period. what could it be???? thanks !!!