Not heard of treating simple tendonitis with antibiotics.
Is there a reason why your quack hasn't recommended a NSAID (such as ibuprofen) ?
More general information at
http://www.cks.library.nhs.uk/patien...let/tendonitis
As regards preventing it happening again, you need to avoid the cause, and strengthening the surrounding tissues (by something such as swimming) may help- but complete rest for now.