What is wrong with my stomach? HELP!?

OK. Last Friday I was rushed to the ER. I was having horrible cramps and nausea. I was throwing up yellow foamy vomit. I had just started birth control and my period the day before. When I was at the hospital they really didn't say what was wrong. They gave me pills for stomach acid and nausea, and a shot in the butt for cramps. They sent me home the same day. Since, I have been having nausea BADLY I feel as if I'm going to vomit at any moment (especially in the morning). I am extremely tired and have been on my period for 10 days. ( VERY UNUSUAL) It's a very faint period but it has yet to end, and the blood is a brownish color. I believe my doctor gave me a pregnancy test a week before and I'm sure they did at the hospital as well but the didn't tell me any results. Could I be pregnant? What do you think is wrong? Help me please.