im no dr. and had it numerous times (not over the last 2 years though – so touch wood)..
i could physically tell when i was getting it, first have an off tummy then legs start to go achey with a slight sore throat, within half a day of the sore throat starting my throat would go mega red and tonsils swell, at this stage i always immediately got to a docs, and MADE him prescribe antibiotics, i always catch it at this stage (luckily never falls on a weekend), and the antibiotics have stopped it mutating into full on tonsilitus (where you are stuck in bed with white spots on your throat and failing to eat/drink a thing)….honestly get to the docs and ask for some before it settles in! ive done this the last 4 times i had it, learing from the first 2 occasions where i didnt go the docs until i was bed bound and off work for nearly a week :(, catch it earlier and the worst you should get is a bit of a sore throat and achey body, but i managed work on all those occasions since catching early!
edit : before anyone states it wasnt probably tonsilitus – it was on all occasions, i had tests at the time and i had tests to see which anti-biotics will work on me – i guess my doctor is quite easy to get them out of 🙂 worked though!