Why Am I So Scared To Have A POOP At School? ***PLEASE READ DETAILS BELOW***?

I'm having problems at school. I hate the thought of going for a poop there. Everyday I wake knowing I have to go to school and I practically burst into tears.I told my mum it was a stomach pain and now and to this moment now she still doesn't know that it's me worrying about the toilet! She wants me to see a counsellor to get to the bottom of this supposed "pane". I have been trying to make myself go in the morning by eating fruit, exercising and drinking plenty of water. And now I think the more I think about it the more I need to go to the toilet. Is this possible? HELP! ----- P.S --> I have been worrying so much about it that I have even missed school and my maths grades have dropped (I'm meant really good at maths) because I have missed so much school!