Can I prevent unwanted items from appearing more than once in the same playthrough?

The "drops" are completely random. There is no way you can force an item to NOT drop, but you can mitigate your chances of getting a duplicate:

• unlock everything you can. Characters' primary and secondary secret items, secret bosses, basically you have to play A LOT. Having to choose from a pool of 20 items is different from having to choose between 130.

• unlock the D6 by:

  beating the Womb with ??? (that is unlocked by beating the game 10 times)

This item lets you re-roll your unwanted items and with some clever combinations and tricks, grants you almost any item you want.

Yes, it is possible to force it not to spawn again in that playthrough.

If you collect an upgrade, it stops spawning until you start a new game, so the way to stop teleport from spawning again is to collect it, and then get your old activated item back.

Pick the item up, then pick up your old item again. Touching a space bar item will remove it from the drop pools for a run.

As far as I know item drops are totally random so, as I see it one of 2 things is happening. 1.You just have really bad luck and keep getting the same item 2.Your game is glitched and keeps spawning teleport.

EDIT: Reinstalling your game may fix this error.