What Causes Light And Short Periods Despite A Negative UPT?

I have a question, I seriously think I m pregnant but i don t know forsure! I m so frustrated, the past couple weeks in the night, and during the day I feel these almost type flutter feelings, well just last night I was paying very close attention to my stomach, and I had my hand on it, where my abdomine sorta is, I felt very light thuds, almost like these very tiny tiny little kicks, I almost know and feel that my body s pregnant, I litterally sit there quietly, with no one around looking at my stomach and there these little spots bearly BEARLY moving up and down like. I m very frustrated bc the past 3 months I ve had very abnormal periods and there very very light. They will go for 5 or 6 days almost like spotting, then stop for 10 days and happen again for maybe 3 days, and now I hadn t had any type of bleedi g for about 9 days and today I wiped and had brownish reddish spotting like, I ve taken about 8 pregnancy tests and they all are negative, I m trying to get a blood test but I just moved out here to tucson alone and I m 17 about.to be 18 next month and I have no insurance. I m trying to look into getting a blood test or ultrasound but given I don t have insurance I don t know how I d do that as soon as possible without such a high bill