Did you have unprotected sex after having your period? If so, you could be pregnant, but it would be awfully early to be having any symptoms right now.

I doubt you could be pregnant from intercourse before your period. It's highly unusual to have a regular period and still be pregnant. Some women mistake spotting around implantation as an unusually light period.

It could be that you are ovulating right now? I notice every month when I ovulate, I get very nauseous around ovulation. It has even made me throw up. I have run across lots of other women with this same issue of nausea around ovulation. Especially if you've been having a lot of discharge that is watery or stretchy and resembling uncooked eggwhites, you are probably ovulating. It would be about the right time in your cycle for this to occur if you have regular 28 day cycles.

If your period is late, you can take a home pregnancy test then.