You should go to the emergency room, even if you can't afford it they will still see you and just mail you a bill that you can pay off slowly. It will put your mind at ease and they'll help you faster than a doctor appointment will. Good luck! Even if you aren't prego, don't be discouraged! Trying is the fun part! =D
You need to go get blood work done so you can do what actright said and go to ER (tell them you had a couple positive pregnancy tests but have been bleeding) or call your doc in the AM and ask them for one. But if you go to ER they may try and do an ultrasound as well.