What Causes Missing Periods, Spotting And Abdominal Pain?

Last may I took pills to delay my period and it cAme normally after 3 days I stopped the pills.last month I hAd a 3days delay, but this month I have a 10 days delay. I did it twice the pregnancy test and twice was a negative result.now I am seeing a pink discharge for 3 says and low abdominal pains.