Irregular Periods, Lasting 4 Or 5 Days With Lower Back Pain, Bloating And Cramping, Spotting And Back Pain After Periods, No Sex. Pregnant?

Hi, I m 19 and I usually have irregular periods sometimes I get them the 25th or 26th day after my period and other times I get them the normal 28. I got my period on May 26 (the 27th day) but two days before (May 24th) I had experienced lower back pain , I was bloated and had a bit of cramping. May 25 I was normal and I got my period very late at night the 26th maybe you could say the 27th. My period usually lasts from 5 to 6 days and it starts with light brown blood lots of cramps for about three days, the second and third is a bit of a heavy flow, the fourth is light and the fifth and sixth is usually spotting (brown blood). This period though last 5 or 4 days, it started out like usual, the second day it was a bit heavier than normal by the third day it was very light, the 4th was spotting barely nothing and the 5th was almost nothing. Yesterday my period was gone but today I noticed a bit of spotting brown blood and lower back pain. I haven t had sex for about three weeks maybe almost four (I m not sure) could i be pregnant?? What s wrong with me?? I m so confused!