Could I be pregnant or just paranoid?

Okay I'm very scared and nervous right now, I'm a 18 year old girl who is sexually active with my significant other. I am on birthcontrol and have been constantly on birthcontrol since I was 15, I'm very strict about the time I take it. Now my last period lasted two days and was very light, by very light I mean could barely consider it spotting. Now I have been feeling sick to my stomach and been urintaing a lot along with (I believe) slightly darker areas around my nipples. I'm scared I could be pregnant. I'm not ready for a child but I would keep him/her and I would love him/her very much but I'm scared. I don't know what to do. I'm going to take a test Saturday but I can't sleep and I feel extremely sick to my stomach.