Im on the pill& had unprotected sex 7days ago. my period was expected mon, but came tues( a day later)it's also not as heavy as normal. am i pregnant?

Your hormones are in: .. flux for some reason. Irregular periods and spotting could mean you may have some hormonal imbalance that could be affected by many different factors, including age (if approaching menopause?), nutrition, illness, exercise (or lack of it), body girth, psychological well-being, stress, season, or simple fluctuations of other related hormones (thyroid for example). Check a pregnancy test too.

Odds are low: Birth Control pills are ~ 90% effective in preventing unplanned pregnancy. However, if you think you could be pregnant, do a home pregnancy test to give yourself some reassurance. Nausea could be due to other reasons as well.