If you are not seeing those custom lists under the "add to list" button on an item listing, or under the "Watchlist" heading on your Watch List page when using a desktop browser, sometimes signing out of your account and signing back in can make a difference. Or try another desktop browser.
If you still have trouble accessing your lists, you should be able to see all the items on all of your lists at once using this link:
https://my.ebay.ca/ws/eBayISAPI.dll?MyEbayBeta&SortOrder=ASCEND&GotoPage=1&MyeBayListIndex.Filter=Al...
If you are able to add an item to one of your lists, you should be able to reach that list from the item page, using the link in the blue band at the top of the page where it says "added to your LISTNAME list | Remove", where LISTNAME is a link to that list.