Could i be pregnant? Please help me.?

I came on my period on the 4th April, i then came off on the 12th April. I had on the 16th April and im not sure if i was ovulating that day ive done the ovulating calculator and they all say something different. Anyway i had a few days before that too and im just a bit weary if im pregnant! I have symptoms of: Back pain, bloatedness, nausea, i feel sick after eating, random shooting pains down my uterus, tiredness, and sometimes i feel like im about to come on my period but im not due untill the 2nd May. I also had a bit of brown discharge on the 21st april - 24th April and not sure if this was implantation?? Please help me i would really appreciate it...