The rules state:
Event cards are shuffled and dealt. Each player recieves three Event cards. Players look at their cards, choose one Bonus card that they keep, and discard the remaining cards. The Bonus card that was kept should be kept a secret from all the other players. If a player recieves only Discovery cards, he should show them to the other players, discard them, and receive three new cards. This is repeated until such a player recieves one Bonus card.
(The bold section was highlighted by me)
Therefore - I read that unless you receive all Discovery cards you simply choose from those you have, be it 1, 2 or 3 Bonus cards. You only get a new set of 3 cards if all of your original 3 cards are discovery cards.
I hope this helps!!
Have fun with this great game!
EDIT - and of the three cards you are dealt you only get to keep 1 Bonus card, the other two cards are discarded.