Welcome to this forum.
Regular and strict use of contraceptive
pills prevent 80 - 90% of unwanted pregnancy
.. Hence if you are on the pills and are very regular with it, there are less chances that you can get pregnant, when compared to those who are not on pills or on irregular pills. So you need not worry.
If you have any of the pregnancy symptoms and still have a doubt, you can consider getting a pregnancy test, Or you can post your symptoms here for more specific suggestions..