Could I be Pregnant ?

I am on birth control, Ive been on for the past 5months, I've been taking it correctly - I did have a lott of mistakes last month, bc i was sick and was on antibotics and had picked up my new pack 2days late.. - but this month Ive been doing great about it. Ive had unprotected sex 3 or 4 times this month resulting in him ejacuating in me, and Now I realise how much I am not ready to take care of a child.. according to my birth control [loestirn 24] I should have started yesterday, my color pills began then... today I still havent started and I have no signs of starting.. I know stress can cause late periods so I'm trying not to freak out quite yet, also my boobs feel the same , i havent had nausea , I have been more sleepy, but I just graduated, so i figure thats the reason for such. i d k but i don't want to buy a test and stress my boyfriend out If I'm over reacting like i tend to do a lot... so PLEASE HELP ME