Weird pains in stomach and possible back labour

So the past couple of months i have been expierencing sivere back pain. I am not usually one to have problems with my back and lately its becoming so bad that its very frustrating. It almost feels like im always pulling my neck down to make it crack or twisting and turning to do the same. No matter what there always feels likes theres something in there or that i have to constantly be stretching it until it almost breaks. Iv had my periods but i find they have been late, last week i started wednesday early afternoon and it started to really slow down the next day, i had one time when there was alot, but only lasted 20 mins at the most, then i finished saturday night and it was completely done sunday. I missed my pill sunday so i had to take 2 on monday. Iv heard of people in my school being pregnant and having their period but not getting that big stomach wise, nor nausea. I do sometimes in the afternoons and nights feel squamish to the point where i could throw up if i initiated it. Also the girl i know that was pregnant like that but didnt know was told after she had the baby that the reason she had so much back pain and didnt get very big in the stomach was bc the baby was in her back for most of the time, so it being there was mistaken for back pain. I took a pregnancy test before which was 3 months or so ago and it was negative. I didint bother taking another one after i noticed the back pain bc iv had a light to moderate period so i didnt see hte point. I may just be paranoid but i just want some input before i go crazy! So, could i be pregnant like that girl and the babys just in my back?