It's ok to post how you feel.
Go to your teacher / tutor and tell them that you have been worried about your test results and ask them if they would spend some time with you explaining what you need to do to get the grades that you want.
It might just be that you need to be clearer about how you phrase your answers and make it easier for the person to be able to give you the marks. It might be that you have the wrong end of the stick for some theories and they can put you right. If it is essay questions, it might just be the way you layout the argument.
I'm sure any teacher would be happy to help you. After all they want you to succeed too!
If it is any consolation I got a U (so bad it is ungraded) for my Mock biology A-level. I passed with a B - so it can be turned around
Also as well as study get in some fun time too. If you play sports it wouldn't hurt to go and do something physical to release all that tension energy too.