It really could be a whole lot of things and it would be irresponsible to try and give you the impression that a sensible diagnosis can be made. But here are a few illnesses you can try and see whether they fit:
Meningitis: you would very probably not be able to bend your head forward (to touch your knees) because the pull on your menigae when doing this, which normally isn't felt would give you a really bad pain. You would possibly also become desorientated
Mononucleosis: probably your liver (below ribcage, right hand side) would be swollen and palpable or even tender. You might have swollen lymphatic glands under your arms, under your lower jaw, in your groin. You would be feeling very ill.
Scarlet fever: usually a red tongue and a white triangle around mouth. Sore throat, high temperature, feeling of severe illness. Antibiotics will be given by doc.
Influenza: comes on within a few hours (feel fine in the morning, half dead at 2pm), temperature, aches all over
As I was saying, no way to diagnose you. But I suggest you keep in bed, take in as much fluid as you can (herbal tea, water), very light meals if at all. Get someone to look after you. Go to the doctor's on Monday straight away. If it gets worse, go tomorrow or today. Better pay, than regret not having gone.