You may want to check your tire pressure for your tires also. If you are getting "SNAKE BITE" flats these come from having too little air in your tires and the weight of you and the bike compressing the tires into the rim causing the classic snake bite flat.

Now the screw in the tire. That's an odd one. Could have happened in shipping. Many bikes have little air in the tires when shipped and a screw could have migrated inside the casing. If this were on a NEW bike the Dealer MIGHT replace the tube for free. If I were in that position as a shop mechanic, I would look over the inside of the tire to look for rust marks which would tell me that the screw was indeed in the tire when new. A tube could make or break Customer relations and it would go a long way to keep a customer.

Chris