It's impossible for us to say. As we don't know if this is just an "I don't feel like school today", in which case you should push yourself to go to school.
Or whether it's something really serious that deserves to be escalated via your GP.
Also, you've got public examinations coming up in the next few weeks - and possibly one today?
One is almost never fully prepared for these exams. All you can do is your best between now and the time that they start. If your best isn't Grade A, don't worry about it. Academic success is not a requirement for success in life.