Still not ready to be a mun

I had sex with my boyfriend last Friday 29th of April. I took 4 tabs of contraceptive pill which is Nordette. Then I didn't take the second dose after 12 hours because my heart palpitate. A week ago I feel very tired and I'm having mood swings. And I think I have this 'withdrawal bleeding' or 'spotting'. I can't understand. Is it possible that I'm pregnant or is it just a side effect of the pill? Answer my post asap and please share your experience. Thank you...