What Causes A Missed Period?

Hi, I have pcos. and i was taking clomid and progesterone pills every months for getting ovulation and periods on time. This month i stopped taking clomid and progesterone pills. And I Ovulated by my own without clomid. but didnt get my periods... after progesterone pills i got my periods after 35 days. Today it is 1 week late still didnt get periods..I did home pregnancy test 3 times ( 2 tests 5 days sooner and 1 on 1st day of my missed periods). I have sticky white discharge sometimes. What to do now? When should i use home pregnancy kit ..or can i get pregnant or not? pls.. help me m very tensed.