Don’t worry breakthrough bleeding and missing a period is completely normal on the pill, especially in the adjustment period (3 months).
If you’re on the combination pill you have a 12 hour window in which you can take your pill and be protected, so even if your bf finished inside you, you will not get pregnant.
Read your pamphlet, learn how to take your pill correctly accounting for things like sickness, missing pills, antibiotics, etc. and read up on side affects and how it works so that you can trust it more.
Don’t get freaked out by ‘pregnancy symptoms’ either, the side affects on the pill are the same, you only need to take a test if you have took your pill incorrectly and had unprotected sex or if you miss two consecutive periods.