Something is wrong.. I need advice?

I don't know what this could really mean. My lower stomach feels very bubbly, but not like "gas" it just feels like a pitter patter, or a tapping. I have been having to go to the bathroom (if you know what I mean) a lot. And have also been having lower back pains, and rib aches. I threw up today, a little bit. But I just had 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 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... I have also been getting a lot of headaches lately.. Please help me, with maybe some possibilities of what culd be going on. I am a 19 year old girl.