How can I find out why my contributions are deleted at wikipedia?

Try looking through your talkpage, othso. If there are any messages along the lines of "Hi, we've deleted your xxx contribution because zzz...." (xxx meaning some contribution or other and zzz being the reason for said deletion) then that should give you a fair idea of what's going on, as Marvin said. Alternatively you could perhaps come to the conclusion that you're simply not welcome there and do something else instead. Hope this helped.

Edits on a page that has been deleted will show as deleted. There is no good way to trace them other to know what you have worked on. Deletion discussions are a good way to determine which they might have been. If 626 individual edits had been deleted, you would have been notified.

They are absolute behaviour problems over there. I quit making entries & fixing.