Maby pregnante help please?

okay so im 15 1/2 been on birth contorl about 6 months for the past 2 weeks every thing has been diff.. i got a very light spotty period ( sooo not normal for me mines usualy very heavy and painful) back aches slight cramps feeling sick (throwing up in my mouth sometimes ik eww) green stool headaches every 5 min and feeling the urge to unrinate all the time.. when this started i did miss 2 days of my birth control last month. my boyfriend me and a friend of mine are worried i cant afford a prego test..could this be a pregnancy or something else please every one help me i am like freaking out majorly.what do i do????/