One way
to increase topics in conversation is to do things together - like
what I had mentioned above. Take part in courses, interest group,
arts, music or even foreign language if both has the same interest.
This will boost greater communication in long term.
Second - keep making mutual friends. The more mutual friends you
both have, the more things you could talk as well. 
But seriously speaking, in your case, its not so much about the
conversation part - its about your desire of wanting those
sweet-lovey message and stuff to return or at least maintain at the
usual level you used to have it:
If it is not within his/her personality to do that - generally,
such 'boons' would be short-lived and would reduce in frequency
over time. What I meant is that unless is she what I termed it as
'Disciplined Lifestyle.' (Someone who is consistant in his attitude
and behavior towards his relationship by demonstrating a set of
'actions' he/she will do regularly. E.g. SMS, phone everyday, etc)
- if not, unless you truly mind this aspect, a little communication
would whip up miracles when done correctly and strategically.
Talk to her about your feelings and thoughts. Share them. Again,
this is another form of conversation that would build your
relationship and foster better bonds as well.
P.S: Don't always compare past and present - this is one mistake
everyone does. Time change, world change, love change. We have to
look at every factor around our relationship before we proclaim
that a problem is going on. Everything ain't stagnant - it's
constantly moving, either go up or go down.
Cheers
