SOMEONE WITH GREAT RELATIONSHIP ADVICE NEEDED!!!?

Alrigh my gf and i was talking earlier, and she seemed to txt awkwardly, not the same as usual. I told her she wasn't txting like she usually does, and asked if i was annoying her, she replied "ur not annoying me lol iv just thinking about something today". i asked what she was thinking about and all she said was "nothing important." she promised me it was not important and i told her she can talk to me about anything no matter what it is. and i know if it wasn't important she wouldn't have said anything about it. :\ she kept promising it was nothing and her friend who's house shes at currently txted me and said she was fine. i asked her is my gf told her to say that and she said "she told me to tell you cause you won't believe her" all i said was that i believed her but was skeptical about it. Anyone please help me im worried and dont know what to do at all :| shes my firest gf and im her first bf so i really dunno,