It's strange, I know it should pass but why is this happening?

At first we could not shut up and were speaking online none stop ant it became something diffrent then just a friendly relationship. I live in Norway and she lives in Lithuania(baltics) so when we are apart we talk via skype.
After 18 days she will visit me here in Norway. So that kinda shows commitment but now when we talk via skype I just don't have what to say to her, it's not like i'm bored with her or something negative it's just like i'm blank , the feeling is interesting and good in some way but it really starts to annoy her and she i think suspects that i am cheeting or smthg else.
Please comment ,advise :)

I have to leave home once a month for a few days, and often we'll spend hours during those times with Skype up, or on the phone, saying absolutely nothing to each other. It's comforting just knowing she's there, hearing her in my bluetooth, seeing her putter around the house, studying for an exam, or making dinner, or whatever. Sometimes silence isn't about not communicating, but about not needing to.