My period is over 1 month late. And today I had one pretty big brown clot. But no bleed, or spotting at all. I took 2 test and both negative.?

Miscarriage. you may have had a miscarriage. many women have far more miscarriages, for different reasons, than pregnancies that come to term. although you should have your period soon, if this remains a problem, please see your primary care provider.
Exam time. See your doctor for an exam - somehow you are not having normal ovulation cycles and discovering the cause is the way to start solving any problems. There's no sense trying to guess what the 'clot' was or whether it was part of the missing periods - have an exam and maybe lab work. Learn what you can - ask questions. Take care and you'll probably be okay soon.