Hello,
Welcome to the ehealthforum. Your concern is the delayed periods or missed periods. Delayed or missed period is known as amenorrhea. Apart from pregnancy, there are many other reasons for a delayed period.
The other causes are hormonal imbalance like in PCOS (Polycystic ovarian syndrome), stress, obesity, malnutrition, anemia, hypothyroidism, illness, etc. The only way to know whether you are pregnant is to get a pregnancy test done. You can do a home pregnancy test by using a pregnancy kit easily available at chemists but it should be done after 1 week-10 days of your missed periods. Alternately you can also get a serum HCG test done.
I hope it helps. Take care and regards.