I got my period 3 days late and so far it's normal. i took an at home pregnancy test 30 days after sex and it was negative. could i still be pregnant?

Not likely: All signs are pointing to "not pregnant". 30 days after a single intercourse episode is definitely long enough to know if you have conceived or not. Home urine tests for pregnancy are very accurate these days. There is a natural variation in menstrual cycle length. I wouldn't be worried if it was just 3 days late. If you're still worried you could always try a different brand of preg test.