What Causes Delay In Periods?

"2 months delayed"
My last sex was in the month of february and then first week of march I took a pregnancy test and it came out negative, and then after 1 week, my period came. (it was a normal heavy flow of menstruation). Now for april & for this month of may, i haven't had my period yet. so meaning I'am already 2 months delayed. 3 days ago I took a pregnancy tests, (1st urine in the morning) the result was quite confusing because i don't know if it's positive or negative. the other line that came out was very light and it was quite outside the window so I bought another pregnancy test and it is the one you can use any time of the day. I used it at the same day(afternoon) and it came out NEGATIVE. no more another light line that came out, it was just plain negative. I'am really confuse now, because my last sex was in the month of february and in the month of march I had my period and then for the month of april and for this month of may I haven't had my period yet. am I pregnant? or it is just a hormonal imbalance? please help me its quite stressing me out.