I would suggest you get to a physiotherapist and also your GP for an appointment to review a few issues. Firstly a full blood test to see if there is anything out of the normal causing an inflammatory response and secondly to look at you mechanics.

If all your current investigations are clear then could it be that you have been bitten by something and have suffered an allergic reaction? Look closely around your leg for a bite, perhaps with a magnifying glass.

For the record I don't understand why you would keep this issue from your parents? Are you about to start training as a PT student?