I started the 2nd packet of my combination pills a day late. i had unprotected sex on the 6th day. what are my chances of getting pregnant?

Possible but . . .: You can always get pregnant from unprotected sex. Sexually transmitted diseases/infections, too. Skipping/forgetting a day (or starting a pack a day late) shouldn't make a big difference as long as you double up as soon as you realize you skipped/forgot/etc. If you're really worried, there's always emergency contraception. But just picking up where you left off should be fine. Set reminder on phon.