flask: relative root in submit form

I tested my application with internal flask web server,
after that I move things to nginx and uwsgi as described here:
http://ift.tt/146BpA6

So now flask app become available not from:
http://host

but from

http://host/myapp

all works fine, except POST, in html template I have something like

<form action="./" method=POST ...>

when I press button (on page with url: http://host/myapp) I redirected to URL: http://host, but I need redirection to http://host/myapp, how can I achieve this?

Also I want my code to work as "http://host:5000/" for testing, and http://host/myapp for production at the same time, so I do want to change form action URL to something absolute.

May be this is not problem of flask, but I should modify nginx rules to change post url on the fly, or I just use wrong html code, as I new in web programming, I can not get where I wrong.