Your chord progression fits in to the key of B-minor.
i - ii° - III - iv - v - VI - VII
Bm-C#°-D-Em-F#m-G-A
First we translate the chord progession to diatonic function scale degrees.
Bm-A-Em is then i-VII-iv.
Scale degrees can be grouped to three harmonic functions
Tonic i, III and VI chords
Subdominant ii and iv chords
Dominant v and VII chords
Your chord progression i-VII-iv translated to harmonic function is
Tonic-Dominant-Subdominant
That is what you have. How to proceed from here?
The subdominant needs to be resolved. For instance you can create a harmony
Tonic-Dominant-Subdominant-Tonic, which in practice leads back to i (Bm) chord.
Another possibility is go from Subdominant to Dominant, and resolve it to Tonic
Tonic-Dominant-Subdominant-Dominant-Tonic
That gives two possible chords to follow Em, the v (F#m) of VII (A) chords.
Sometimes in minor keys the v chord is replaced (or borrowed from a harmonic minor scale) with the V chord, which sounds sometimes better than minor v. In the key of Bm that v->V would be using F# (major) instead of F#m.
Or you can take a look into a voice leading and using a secondary dominants. Whic is discussed on this topic
https://www.guitartricks.com/forum/thread.php?f=3&t=44759
I always think that fuctional harmony theory is only a framework, not the strickt rule.
Let your ears decide what sounds nice in the context.
Good luck for the song writing. Have fun!
