I think it is possible to be pregnant but still have (what appears to be) a period.

Some ladies do have high levels of hcg in their urine/body too which might influence your test and your feelings of nausea.

Then again, you might be having twins!!!

Lucy (mod) might be able to help you out - she had really high levels of hcg and her bfp nearly jumped off the stick lol and there was talk (until her ultrasound) of her having twins! (which she does have a family history of).

Best wishes to you!! Hope you feel better soon!!