hi Imfree,
welcome to the forum..i think ud better sort out first ur birth certificate problem just to make sure everything will be alright before u submit ur application for a fiancee visa..
because on the checklist of requirements, birth certificate of the applicant is also necessary..
i remember there's a post here about failed fiancee visa application before because of birth cert too, u can use the search button here to check it..
i hope everything will be fine with u soon so ull be able to join ur fiance in UK..
Goodluck and God bless..
Kimmi