IT is very hard to answer your question as you did not mentioned other symptoms like stomach ache, diarrhea etc.
There is a lot of nausea reasons. And yes, you can be pregnant. Slight bleeding can appear when an embryo is implanting in uterine wall, and it can be thought as a normal period bleeding.
Other very common reason of nausea is peptic ulcer
stones, "stomach flu", stomack acid reflux
and many many others.
You should have pregnancy test, blood tests for inflammation, hepatic and pancreas tests, abdomen ultrasound
and gastroduodenoscopy performed at first.
Hope this will help.