A: If you’re asking if you can interrupt the completion of your Draw phase to play a card that requires the discard pile, and the answer would be no. You need to complete your Draw phase before playing anything. In this example, let’s say the draw pile contained two cards, and it was Draw 3. You’d have to draw those two cards, reshuffle the discard pile, and draw your last card. Then, and only then, could you start playing cards from your hand.
If, however, you’d completed your Draw phase, and it ran the draw pile out exactly you should technically not reshuffle the discard pile until someone needs to draw more. So if there were three cards in the draw pile, and it was Draw 3, and you drew three cards, the discard pile should technically be left in place until you, or the next person needs to draw again. In that case there would still be a discard pile for you to use with various card plays on your turn.