I have created a Facebook fundraiser but my previous donations aren't showing on there.

Unfortunately, there is a bit of a glitch in the Facebook system where any donation that is made prior to setting up your Facebook fundraiser won't reflect on your Facebook fundraiser page, and I believe that may be where your issue is rising from- however once set up and linked (as yours currently is) any donation made will reflect on the fundraising page accurately.

 

You can always share your fundraising page as a link on Facebook if this is easier as well.