Well ... I tried to find something with this new hint of "Sweden", but even with this keyword added mostly all pages that turn up in Google have some connections to Albania and Albanians...
It's funny that even a search for Mertis turns up a city in Albania:
http://www.behindcity.com/explore/albania/fier/mertis/
But also in Albanian the name seems to be quite rare, with no info about meaning in sight.
This page here:
http://names.whitepages.com/first/myrtezallows to check the number of people in the US with Myrtez or very similar given names. Among the variants given Myrtice is the most popular today by far, which resonates with the guess of a poster in your first thread, with Myrtice as a variant of
Myrtle.
However, I somehow doubt that a rary English name variant of
Myrtle turns up as a rare name in Albania, which means that we are probably not yet closing in on your mystery.
Rene www.BabyNames.ch