Could I be pregnant? OR is it something much more serious?

I have had feelings in my stomach lately, that fees like a pitter patter, or a tapping. I've been getting a fair amount of heartburn and a lot of headaches. And have also been having lower back pains, and rib aches. I threw up, a little bit, yesterday. But, theodd part is, I had what seemed to be my period about 2 weeks ago, and before that, I had been having the same types of symptoms, leading me to think I was pregnant. I took a few pregnancy tests. in the morning even, and they were all resulting in negatives.. I then got my period. I know you can sometimes continue to get your period during a pregnancy so I am not sure I can completely rule that out. Please help me, with maybe some possibilities of what culd be going on. I am a 19 year old girl, and I have no health insurance so I can't just get up and go to see a doctor.