when to worry about pregnancy on the pill?

i’ve been on the pill for over a year never missed one (latest 2 hours late) and sometimes I still freak myself out and think i’m pregnant. :/. how would u tell if u were pregnant? I had a withdrawal bleed since I last had sex without a condom (he didn’t even cum in me either) but I had weird breakthrough bleeding that month before my normal withdrawal bleed. I now decided to use condoms to be extra safe. should I not worry since I had withdrawal bleed and am using condoms? I just wanna know what would happen if u were pregnant on the pill.