My foreskin always pushes the condom down and causes it to crumple up.

Sometimes the foreskin isn’t totally tight when erect, and that’s okay. One thing you can try is adding some extra lube to your penis and actually rubbing the condom up and down a couple of times (once it’s on) to get your foreskin up INTO the condom. The lube will allow for easier movement of the foreskin under the condom and should help prevent crumpling/bunching.