If you had sex during this time, then of course you could be pregnant. You were not on the pill long enough to be protected.

However, bleeding is usually a sign you're not pregnant. Seems a lot of girls get a messed up period after stopping birth control when they shouldn't and automatically think they're pregnant.

It can take up to three months to adjust to birth control. Four days wasn't long enough. You stopped it incorrectly so of course you're going to have wacky bleeding.

If you were nauseous, you should have changed when you took the pill. Some women get sick if they take it at night, and some get sick if they take it in the morning.

If you had unprotected sex (as in, no condoms or anything), yes you could be pregnant because pills aren't effective at all if you only take them for four days. Pills take seven days to be effective.

You should generally wait longer (like a few months) for side effects to clear up before you give up on a pill. Unless they are really severe, I guess.

Of course, your lengthened period (or light period or whatever you had) could be due to taking the pills for such a short time and then stopping. You should take a test if you think you might be pregnant.