My Period Came On 9/12 And Ended Around The 18th.

My period came on 9/12 and ended around the 18th. I had unprotected sex on the 23rd but the guy didn't cum. However, after 3-4 days, i noticed brown discharge but i felt like it was too soon for it to come because it came over a week after my period ended and 2 weeks before my period is due. But it only lasted a day. I took a pregnancy test on the 30th but it was too soon to take it and it came out negative ofcourse. On October 4th, i woke up with a little cramp which lasted like 5 seconds and i felt nauseous like i wanted to throw up.It could be because I was up all night but I've never felt that way before. I am tired all the time but it could be because of school and I have gas cramps like my stomach makes gurgling sounds around my left internal oblique area. Now, (10/6) I notice brown discharge again but it could be because my period is supposed to come. Could i possibly be pregnant?