I had sex yesterday , at the end of the day i started to feel pain in my lower stomach ever since then it's been hurting and i'm dizzy, sign of prego?

Too early to know : If you had sex without condoms or birth control then pregnancy is certainly possible. Use plan b. Plan b works by disrupting ovulation. It should be used within 72 hours of unprotected intercourse regardless of where you are in the menstrual cycle. A pregnancy test should be done in 2 weeks. If the pain does not resolve then you will need to see a doctor.

Get evaluated.: It is possible that you might have had an ovarian cyst which broke during intercourse. This can cause bleeding - and in fairly heavy bleeding, a person could feel light-headed or dizzy. It would be completely appropriate to be evaluated right away - in the emergency room if needed. I doubt this would be a pregnancy related issue unless you were pregnant already. Get checked.