Could i be pregnant?

I had sex for the first time on July 3rd and it was unprotected. I think it was the first day after my period ended. I got something that i thought may be my period around July 20th. I had brown discharge and at one point i used a tampon because it seemed like my period had started but I didn't really have much red blood. This lasted for about 5 or 6 days which is the length of my usual period, although my periods are always very irregular. In fact during my last period i had some brown discharge also and i've had it many times before. I read that you can get brown discharge instead of your actual period but im not sure if that was my period or not. It has been 28 days since ive had sex and i havnt had a "normal" period, just the 5 or 6 days of brown discharge. I do not have swollen sore breasts, i have not been nauseous, or anything else. I feel like i may be a little more bloated then usual but it may just be in my head because its nothing significant. I have not had more frequent urination than usual. For the most part i feel normal but im just really paranoid. Im still able to work out every day, i do not think im more tired than usual although i have had to take a nap pretty much every day but i think that may be because my sleep schedule has been really off because its summer time and ive been staying up later. A couple days ago i would get dizzy when i stood up but that has happened to me many times before and i thought it may be because i drank too much coffee before i had not eaten much. Are there any other symptoms i should be looking for? I tend to over-analyze everything so every little thing makes me think im pregnant. Im 18 and i really can not be pregnant. I am already going through a very stressful time and this just adds to the things that keep me awake at night. I'm extremely worried and really need some advice on what to do next. I have not taken a pregnancy test because i thought it was too soon. I have really no one to turn to about this. Me and my mom are not open about things like this and i dont know who else i could tell about this. Help please.