What Causes Severe Abdominal Pain And Brownish Vaginal Discharge?

Hello, i am very consern. i had my period on the 8th of this month then i had sex on the 14th but my period was like barely on it was only a little pink here and there. when i had sex he did ejaculAte in me and i started feeling sick a few days later its like i am sick to my stomach and my period came back on 16th. at first it looked really brown now its red could i be pregnant or could it be a kidney infection because i am having serious abdominal and side pains?