Why do I always feel this way?!

I have had baby fever for as long as I can remember, it has become a part of my life. 
Having my own child has been my main goal in life, and I hate it. 
I'm 16, and whilst I know plenty of girls my age with children or are expecting, all of the others are getting jobs and choosing uni's. 
I've tried to ignore it for so freaking long. I was 14 or 15 when it started and I felt so alienated. What 14 year old wants a child when they haven't even done their exams yet? 
Over the years it hasn't disappeared, in a way it's worsened, but in others it's gotten better. 
Seeing a pregnant woman or a picture of my old classmates with their babies makes me so envious and I will sit and cry about it for a while, which I hate. It makes me feel so stupid. 
I've started volunteering at a children's centre with the under 1s which is brilliant, as I get to surround myself with babies and watch them to my hearts content, and I also do placement with year 1s. 
I figured that if I surrounded myself with young children and babies I might realise how difficult it is to care for them, I hoped that it would make me turn my nose up at the thought of having one. 
It doesn't seem to be working...
Is anybody else going through this? I'm fed up with feeling like I'm the odd one out, I don't know anybody else my age who suffers this way. 
Also, is there any advice anyone can give me? 
Telling me not to have a child won't work, as I know how hard it is, I watched my mum raise 6 children alone. I've seen how difficult and heartbreaking it is. 
I am taking the necessary precautions to not get pregnant so nobody has to worry about me following through with my instincts. 
I would just like some help with these horrible urges. 
Thank you.