I am trying to conceive . My period's due date was 5th of Feb but now there is no chance of its arrival and I'm feeling pain in my lower belly portion. Am I pregnant?

The only way you know that are pregnant and even a doctor too will only know if you are pregnant if you have a positive pregnancy test.
If you do not have a positive pregnancy test, you are NOT pregnant.
But, this could be also due to Stress/anxiety, weight issues, an elevated prolactin level, or other reasons.
Thank you for your questions.