Late on periods and having discharge. What is the reason?
I am 22 F. I had my periods last month on 16-20.After that, I had sex on 29, 3 and 10(he used protection). Its 19th and I haven't got my periods yet. Also I am always irregular on my periods. On 16 & 17, I experienced light spotting and pain in my stomach which was mild. I am going through stress for past 4-5 days(because of exams and afraid if I am pregnant). I got scared after watching that spotting and took a home pregnancy test on 18th which came negative. When I came home, the same day I saw dark reddish- brown discharge on middle of my panty which was not light like before(about 15 drops if it was spotting).I also experienced same pain when I get my usual periods i.e. lower body, legs and abdominal pain. I thought my periods had come so I used a sanitary napkin. This morning, there was nothing and when I used toilet I saw blood again. It was dark-reddish brown drops and was not as thick as my usual periods(usually dark reddish). I assumed my periods will start today and this is the beginning of it. So I used napkin whole day and again nothing was there. I used toilet and again I saw same blood. I haven't got my periods yet. And did not experienced ovulation during this time. What can be the reason behind this discharge? Please help me out! I am freaking out! :(
(sorry for my English).