Just swapped pills, no period?

Hi, i am 17, sexually active and have been on the pill for 5 months now. Last month i swapped from lenest ed 30 to Brenda ed 30. I always get ny period on the day of the 4th sugar pill. I have been thru on whole pack on the brenda and took my first pill from the 2nd pack last night. I always get my period aroudn midday. Havent got it yet. Is it normal to get a late or no period after just changing pills. I havent gone ome day without a pill. As i said i am sexually active and dont use condoms but make sure my partner pulls out. Is it likely i could be pregnant? Or highly unlikey? Thanks in advanced x